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July 10, 2007


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I was wondering which brand/type of heartworm treatment you recommend?

Dr. Mobley

Dear Joanne,

Thanks for reading. We really only have one option to treat adult heartworm infestations: Immiticide, made by Merial.

For regular monthly prevention, there is milbemycin oxime and the avermectin family. Milbemycin is in Interceptor and Sentinel, made by Novartis. Ivermectin is in Heartgard 30 (made by Merial) and various generics, such as Iverhart. Selamectin is in Revolution, made by Pfizer, and applied topically.

There are other products. These are the ones that I use to provide a variety to my clients. There is no one product that is best for everyone. Some give intestinal parasite control as well, so give flea control as well. Some are easier to administer for one dog, others for another. I believe them to be equally effective, so it's a matter of what works best for you and your dog.


Have you ever heard of heartworm treatment affecting a dog's behavior? We adopted a rescue dog a couple of months after he was treated for heartworm (he ended up losing an eye because the second dose wasn't administered in the right timeframe) and we're having some severe behavioral problems. Just wondering if this could be part of it.


Heartworm treatment generally causes problems in the lungs, via the damage to the blood vessels that supply them (the pulmonary arteries). The period of recovery while the worms are being dissolved can certainly be stressful for the dog. Generally speaking, I have not seen any changes in the dog's personality and behavior after recovery.

I would not be surprised if the dog were having trouble adjusting to the loss of an eye, but I am puzzled as to how this occurred. I have never heard (nor can I find in a search of Veterinary Information Network) of a similar situation. Ivermectin is generally used at the end of treatment to clear the baby heartworms from the bloodstream, and ivermectin toxicity is known to cause blindness, but this is usually in both eyes and is usually temporary. I have never seen this myself, but it is reported as a consequence of overdosing (or in a dog that is exceptionally sensitive to the drug).

I would be interested in more information as to how the blindness developed.

Mary Lee

I have a 3 year old great dane that I recently rescued from a family that "didn't have time to take care of him." He is heartworm positive and I took him in to start his "Immiticide" treatment this past Monday 2/7/08, and was told if everything went well he should be able to come home on that Wednesday 2/9/08. Long story short: He is still not able to come home as of today 2/14/08. He has had a "very severe reaction to the injection" as in the injection site itself. My veterinarian says that he has never seen a dog react this severely before from the actual injection. His whole pelvic area is completely inflamed, his white blood cell count is extremely elevated, he is in sever pain and cannot even get up to go to the bathroom. I can't even type this without crying. I feel like they are doing everything they know how to help him. They have him on an IV for fluids, a strong antibiotic they started today, and "tramadol" for pain. Any suggestions?

Mary Lee

Correction to recent post. My dates are messed up. I brought him in for treatment on Monday 2/4/08 and was supposed to be able to pick him up on 2/6/08. Today is 2/11/08.

If they're is any advice you may be able to give, I would greatly appreciate it. It seems that since it is uncommon for a dog to have such a severe reaction there is in turn limited info on it. This great dane named Duke is the most precious dog I have ever met. I am a huge dog lover in general but there is something extra special about him and I will do anything I can to help him. I love him very much.


Hello, Mary,

I am sure that your veterinarian has already called Merial (the maker of Immiticide) to report the reaction and ask for their advice.

When Immiticide first became available in the U.S., Merial sent out mailings, including an instructional video on giving the injections. The injections are given deep in the epaxial muscles (the long loin muscles on either side of the spine), using a 1&1/2-inch long needle to deposit the medication deep in the tissues.

I had been using the product for about a year when I had a similar experience to yours. A Rottweiler patient developed an open sore the size of a golf-ball at her injection site. When I called Merial, they asked if I had kept firm pressure on the injection site for two minutes. I had not. They then said, "You need to do that."

The medication is very caustic and needs to be distributed deep in the muscle fibers for absorption. There's really no "place" for it to go -- it just spreads between the muscle fibers to be picked up by the bloodstream. The easiest place for it to spread would be back up the needle track, allowing it to pool under the skin. This produced the bad reaction in my Rottweiler patient. The two minutes of pressure is to try to prevent this creep back up the needle track.

I noted that there was no mention of this "pressure for two minutes thing" in their literature or video [and there STILL is not, and I have spoken personally with several veterinarians who have never heard of this]. They replied, "Yeah, we know, but you still need to do it." Thus, all of my heartworm treatment patients since then have also received a "laying on of hands", and I've had no further problems.

That being said, everything may have been done as well as humanly possible and the dog is having an idiosyncratic reaction, like someone who just can't take aspirin or something. It's not the drug, it's just him. As far as treating the problem is concerned, at this point the care is going to be mostly supportive, as it would be for a brown-recluse spider-bite that causes tissue to die and slough.

Your doctor's approach of Tramadol (a mild narcotic which is usually very helpful and well tolerated) and antibiotics (so that bacteria don't get a chance to complicate the situation by invading the damaged tissue), both sound very appropriate. The only other thing I might be doing would be hot compresses three times daily to increase circulation to the area and speed healing. You might also ask about Lidocaine patches. These can be applied to the skin on either side and give a constant slow release of local anesthetic into the area to help control pain. NSAIDs like Rimadyl can be combined with Tramadol for additional pain relief. NSAIDs should not be used if the patient is already on some form of cortisone for inflammation.

It sounds to me like your veterinarian is doing a good job in a difficult situation.

I hope this information is helpful to you. Good luck and thanks for reading and writing.


Butch is a rescued Malamute and golden lab. mix.He tested positive for heartworms and I was told if the worms were not stage 5 he could be treated. The tests were done and Butch was treated. He ended up with his salivary glands infected and severe pain. He went back for a stay at the vet and was sent home again and now we are being told that he has a blood clot and he is dying and the vet said we should put him down? Why would he have us go through with the treatment to tell us that? The dog has lost alot of weightand his equilibrium seems to be very bad, he can only walk so far without coughing and falling over. Help us Please.


As I mentioned in my posting, there is always a risk involved when you treat dogs for heartworms. There is simply is no way to guarantee success when you have foot-long worms clogging up the works. Most dogs do well, or survive minor complications, but some do not.

I must confess that I cannot imagine how there could be any relationship between the heartworms and the salivary glands. There must be something lost in the translation here.

I am sorry that things have gotten so bad, but I feel that your veterinarian acted in good faith to do what he felt was in the best interests of your dog and for you. Sometimes things just don't work out the way we would wish for them to.

Thanks for reading and writing.

Cindy O'Neal

My Golden has been on the heart prevenative medication "Heartgard" I have never missed a dose and she goes to the vet and is very well taken care of. Today, I took her and the other golden that I adopted to the vet. Red, checkup...and Maggies the adoptee to be spayed. An hour after dropping them off, they called to tell me that maggie had heartworms, and cancelled the spayed. We went to the vets office and then told that Red also was positive...and she has always been on heartgard. Then they told me that we would have to pay for Maggies the adoptee, but Red...Meril would pay for it since we have records of her being on heartgard monthly. What do we do now...these dogs are the world to us. Any advice please


I sympathize with your situation -- more than you know. I'm going to have to post on this one at last, so look in on the blog pretty soon.

The failure of the preventive medicines (ALL of them, not just Heartgard 30) to be 100% effective is becoming a problem. I am told it is primarily in the Mississippi valley, and gets worse as you go farther south.

In the last two years, we have seen a ten-fold increase in this situation. The good news is that we are still seeing just a small percentage of dogs affected, and almost all are large breed, outside dogs. The other good news is that these dogs have very few heartworms present, as evidenced by the fact that none of them have had any significant side-effects of treatment.

While there is no guarantee, the odds are overwhelmingly in your favor that your dogs will do well. Get them treated, send the bill to Merial, and get them spayed afterwards.

Good luck, and thanks for reading and writing.


I am fostering (to adopt) a sweet little girl dog who was heartworm positive and has received the initial treatment (on the 21 and 23 of February). She and her 3 pups were deposited in a drop box in S. Carolina. The treatment was given at a clinic in N. Carolina, and the Vet's guesstimate on her age is 1, I think maybe a little older, lots of tartar, but maybe that's just a poor diet? Anyway she is young and probably had the pups about 8(?) weeks ago. She is definitely underweight, at about 20lbs. She seems happy enough and alert and not without energy, but is not hyperactive. I am trying to figure out how "quiet" she should be kept. Walks? Playing in the house? No activity? And for how long? I want to keep her mind engaged with training, etc... but don't want to get her over-excited. Also, she is sneezing a lot. (not boogery sneezes, just dainty little ones, but a lot, usually after she's been lying down) Does this mean anything re the heartworm, or is it more likely that it's something in my house (she's only been here for two days)? So glad I found your blog!


Hello, Sam,

The sneezing is probably not related to the heartworm treatment. Consider feeding a good quality puppy food while you are trying to help her recuperate from poor nutrition and nursing babies.

Activity should stop short of any prolonged aerobic exercise. Relaxed walking on a leash is okay, any normal mild play in the house is okay. We want to avoid any dramatic or sustained rise in heart rate and blood pressure. This would be more likely to shove chunks of dead worm farther into the arteries, creating a more complete blockage, increased pressure, and potential blow-out, bleeding into the lungs.

It is not possible (nor desirable) for the dog to lie still for six weeks. Just make your best effort to avoid strenuous activity. Call your veterinarian if your dog shows signs of difficulty: coughing, difficulty breathing, poor appetite, fever, or just generally feeling bad.

Thanks for reading and writing.

paula  b

My foster dog who had heartworms was treated with Immitcide and was finally retested for heartworm and thankfully it was negative.
She was adopted, the adopter was told of her HW treatments and that she still had a cough and wheezing if she got excited or ran while playing...My vet put her on prednizone 5 mg bid...and now says to up it to 10 mg. bid....the person who adopted her took her to his own vet...who told him to bring her back to us because she would have problems if not now..but down the road....he did no tests or anything...just from hearing that she had been treated for heartworms and was still coughing and wheezing some. I understand that it takes several weeks sometimes for the fluid and inflamation to go away and that is why you give them pred. I have to take her back because this guy's vet scared him. Whose vet do you think is right? Mine or the adopter's? I am so upset about all of this. I would appreciate an answer or advice asap.
Thank you, Paula B


Hello, Paula,

I would have to say that, generally speaking, the doctor who has actually examined the dog is in a better position to give an accurate assessment of the dog's health.

It is certainly true that the dog's pulmonary arteries and lungs suffer damage from the presence of the worms, both while they are alive, and when they are killed and being phagocytized (dissolved away by the white blood cells). There may very well be permanent problems, in that the damage may prevent the dog from being athletic. However, even so, he may be able to lead a perfectly good quality of life.

I would say it is possible for the dog to be chronically ill after recovering from heartworm treatment, but I would also say that it is not very common for that to be the case. Most dogs lead a good quality of life (even if not "100%"), and are NOT "perpetual patients".

For a more objective evaluation, one could radiograph the dog's chest now and repeat the films in 30 days to see how the condition of the lungs progresses. I believe it is too soon to say what the dog's eventual outcome will be.

I hope this is helpful to you. Thanks for reading and writing.

paula b

Hello, thank you for such a quick answer. I do appreciate that.
I picked Shyanne up today and have her back. She is happy acting...lively...certainly not depressed but is wheezing a lot. I am not sure if the adopter was giving her the pred like he was told or not. I just gave her 10 mg. of pred. Would your advice be to keep her on that twice a day until the wheezing stopped? Also, I have read about Doxycycline and she did not have that prior to the hw treatments nor during them...would it be a good idea in your opinion to start her on that?
My vet, gets a little irritated with clients who get on the internet to read up on things like this. I guess she feels like if a client does this..that they don't trust her judgement as a vet. I just want to educate myself as much as possible. I do realize though...that sometimes people who are not trained and have degrees in medicine can easily get confused and maybe even panic reading too much into something or not understanding it right.
I read somewhere that if the dog's gums are dark red there could be a secondary infection...so of course as soon as I got her back tonight...I looked at her gums...they do seem to look darkish red...not pink. Am I reading too much into this and starting to panic or should I be concerned? My vet is out of town until monday. I have doxycycline here but it is 100 mg.
One more question...until her wheezing stops altogether or at least for the most part...should I try to keep her in a crate or confined area like I did mostly during her actual treatment period. I am sure those worms are still trying to get out of there. Or is it fluid and inflamation making her wheeze?
I will ask my vet for a lung xray next week...is that what I should ask for first?
Thank you so much for your time.
Paula B


Our 5 year old australian shepherd is showing no signs of illness after his his heartworm treament - 2 injections , 24 hours apart. He is home. Nothing more that a little bit of coughing at times. He is doing remarkably well! I thought he was going to be really sick after the injections, such as coughing a lot. Not so! Just after 2 weeks of his treatment he already has more energy. Thanks to an excellent Dr. who put him on all the needed drugs for heart worm treatment:
NOW A HAPPY OWNER OF A HEALTHIER SHEPHERD! He is already showing better quality of life, and it has only been 2 weeks after his injections. Best wishes to you and your companion. They can be saved! Ours was. -jayne

paula b

Hi Doc! I had shyanne's lungs and heart xrayed today..my vet says it looks what she would expect after having heartworm...still thinks she should stay on 10 mg. pred bid for another month because she is still breathing hard..sort of wheezing a bit when she gets excited or runs. She thinks Shyanne should heal some though...anything to add to this? Paula B


I think that the doctor "on the ground" is in the best position to judge the situation. Your veterinarian has probably already told you that you will have to taper off slowly after taking that much pred for that long a time. Good luck!

paula b

Dear Dr.
I have a question about a foster dog I have had since a puppy...she is now about 10 months old. She was brought to the vet by the dog warden because she was tilting her head to the side..he thought she might have been injured. The vet said she had vestibular disease and treated her with antibiotics I think...I ended up fostering her. She has been very playful, energetic, and a happy girl always since then...but usually she still tilts her head slightly to the right side. I noticed the past week she seemed somewhat not herself...not as playful with the other dogs..and was tilting her head to the right again even more so....so I took her back to the vet...she looked inside her ear with the lighted instrument...said she had an infection in her inner ear (or was it middle ear, same thing?) and it had lots of puss in it. She told me to give her 250 mg. Cipro bid...and to recheck in 2 weeks...right now after all of this time fostering her..I have someone actually interested in adopting her....my vet said I should hold off adopting her at least till she gets rechecked. She almost sounds like she thinks something more serious is going on. I have tried reading up on Vestibular Disease on the internet...I just am getting more confused. Should she get an MRI to see if there is a tumor? or is she possibly for some reason more prone to inner ear infections which causes Vestibular Disease or is it the other way around? the disease causes the infections? She is back to her old self already after one dose of meds...playing, running, rough housing with the other dogs. She eats like a little pig and never acts dizzy or sick. Even now with the infection. Any advice you could give me I would greatly appreaciate...especially since she has a good chance of a "forever" home...I want to be able to be honest about her condition.
Thanks so much,
Paula b.


Hello, Paula,

I realize that in a fostering situation it is difficult to spend large amounts of money. However, if there was lots of pus and no eardrum (which I would infer from the statement that there was a "middle ear infection with pus"), the middle ear (tympanic bulla) will need to have any debris removed from it. Otherwise, when you stop the antibiotics, you still have gunk sitting there to start the problem over again. Ideally, the area would have been cultured instead of just starting on the Cipro, but this may not have been an option under you circumstances. You might ask your veterinarian about this, and see if he/she has the instrumentation to visualize and irrigate the area. If not, perhaps he/she could refer you to someone who does.

The doctor who is seeing the case is in a better position to evaluate it than I am, but it sounds as though this dog will have recurring problems if the middle ear is not addressed.

Thanks for reading and writing,

paula b

Hello, this is Paula again about another foster dog that I adopted out back in December.
She is a GSD mix and about 8 months old now. She was the runt of the litter.
I was just told she has Chronic Kidney Failure and Severe Hip Dysplasia. Their vet gave her 2 mo to 2 years to live. She wondered if any of the other puppies in the litter had this (I have not heard so far)and if there would be anything else to do besides diet change. She had bloodwork and xrays done. She is devastated of course. One of the siblings did pass away months ago from congestive heart failure. could all of these puppies from this litter be doomed? I hope not!


Hello, Paula,

It is certainly possible that the other puppies in the litter will have their own genetic anomalies. It certainly doesn't sound like the parents contributed a very good mix for either of these puppies.

I wish that I could give you some useful information, but really, your guess is as good as mine at this point.

Thanks for reading and writing.



I recently treated my 5 yr old labrador for HW. He is doing good and responding well to the medications. I took him in on 6/26 and picked him up the 6/27 evening. Is a little coughing normal? Also hes been panting a lot but its kind of hard to tell whether its bothering him because he always panted before. I know that he's supposed to be crated but is okay for him to be confined in a small area such as the bathroom? he doesnt wanna be in a crate. also is it normal for him to lose a little weight? we noticed substantial weight loss and its only been a few days. thank you so much for reading this...



Hello, Rome,

A little coughing is common, but if your dog is feeling bad, eating poorly, etc., you should definitely let your veterinarian know. The weight loss is troubling. Four or five days post-treatment is when the worms are usually dying and shifting position, causing the dog to feel bad.

A crate is only necessary if the dog is having a lot of respiratory distress, coughing up blood, etc. You don't want the dog engaging in either prolonged aerobic exercise or heavy bursts of activity. The bathroom is not too big.

The key is to have the dog take it easy. You just have to use some judgment as to what will be most effective in that line. If the dog turns cartwheels in the crate, but is quiet in the living room, then go for the living room.

Most dogs would be fine roaming the home, or being walked on a leash.

Call your veterinarian and let them know how your dog is doing.

Thanks for reading and writing.


Thanks for the quick reply. just wanted ask a few more questions. he hasn't had any bowel movements for the past five days. is this normal? i've been feeding him bland diet (boiled chicken and rice) ever since he got home from the vet because he wouldn't eat his regular diet. i find this weird because ever since started his medication, he's been devouring his food. a lot is going i but is coming out. he's urinating regularly. thank you!


Having no bowel movements for 5 days is not normal. It is also not a common feature of dogs undergoing heartworm treatment. You should consult your dog's veterinarian. It is possible that he may want to put your dog on a mild laxative. It should be harmless to add 1 teaspoon of psyllium muciloid powder (generic, non-flavored, non-fizzy "Metamucil") per 20 pounds of body weight, per feeding. Just mix the powder with his food.

Don't forget to notify your regular doctor of your concerns.

Sam Vail

My dog has heart worms, and he coughs once in a while, he's active yet, but has always been skinny, but now his ribs are showing more than ever. My local vet wants about 800 bucks to treat him, but I just can't afford Immiticide. Can I get it anywhere and inject it myself, follow the confinement directions, and then put him on a preventative? He's a 3 year old 60 pound pit bull that my family and i adore.


Hello, Sam,

Immiticide is a legend drug, not available for sale over the counter. Improper injection technique can result in really nasty sore places that slough out (like a brown recluse spider bite). It's also not cheap, even the wholesale cost.

Most folks only hospitalize the dog for the injection, not for the several weeks of convalescence.

You might ask you veterinarian what their fee includes. Our fee includes as many follow-up visits as are needed if the dog has complications (no charge, even if at night), medicine to clear the bloodstream of baby heartworms (later in the process), and blood tests to be sure that the worms are gone. In anticipation of handling these things, we do build some extra into the fee. It's not just the medication.

If you're not happy with your veterinarian's answers, you might seek a second opinion.

There really is not a "roll your own" treatment that will help your dog.

Thanks for reading and writing.


Hello. Three weeks ago I adopted a wonderful dog who came into the shelter as a neglect case. His ears had been chewed I think by mites and he had the early stages of heartworm disease. A week ago he received two immiticide injections which he seems to have tolerated fairly well. He has had also diarrhea intermittently since I brought him back from the pound. I thought the loose stools could be related to the change in his diet when I brought him home, but yesterday he had a pretty bad case of diarrhea and he also vomited a lot. No blood or dark discoloration, just a lot of vomit and diarrhea. My vet thought the problem probably wasn't related to the heartworm treatment and recommended that I give him to a bland (chicken and rice) diet for a few meals. Here's my question - given that my dog was neglected, I am wondering if he might have intestinal parasites and if so, if those would have been killed by the heartworm treatment. I did see something in his vomit that looked like a garden slug (quarter inch thick and two to three inches long)- could that be an intestinal parasite coming up? Thanks very much.


Hello, Nancy,

The thing that looked like a slug may actually BE a slug. It does not sound like any of the common dog intestinal parasites. Dogs will, unfortunately, eat virtually anything that can't outrun them, and a slug cannot outrun them.

The heartworm treatment (Immiticide injections) would be unlikely to cause either the vomiting or diarrhea. The treatment also would NOT have done anything to help rid the dog of intestinal parasites.

You should definitely take a new stool specimen to your veterinarian to recheck that situation - about a tablespoonful of stool that is less than 12 hours hold is ideal.

It is okay to give DOGS (not cats) Pepto Bismol as a symptomatic treatment, and your veterinarian can actually detect more in a firm stool than a loose one. Give about 1/4cc Pepto Bismol per pound of body weight, repeat as needed, as you would for a person.

Thanks for reading and writing.


I have been told, and it has been recommended to me by veterinarians and dog rescues and vet techs I have spoken to online (my own vet refuses to do it, though) that I should use heartgard to treat my 2 dog's heartworms
I live in South Louisiana, and they both tested positive after being on monthly preventative (before I got them..((they were rescues)) so I'm not sure which one was being used)
the theory behind it, as far as I can gather is that the heartgard keeps new heartworms from moving in, while allowing the old ones to eventually die.. slowly, instead of all at once.. which, in effect would eventually leave the dog hw free
is this true? is it really that simple?
I've been told that there is very little risk to this form of "treatment" even though it could take a couple of years to completely get rid of the little buggers, because all the worms don't die at once, thus not creating as bad a problem with the potential for the dead worms causing a clot


Hello, Kim,

Here are the pros and cons of your situation, as I understand them after talking extensively with the "big boys".

It is almost certainly safe for you to give the Heartgard to these dogs, even though they already have heartworms. And yes, even though I am having problems with less than 100% effectiveness, this should still keep the dogs from acquiring any major amount of new heartworms.

As far as the adult worms present, the Heartgard has a pretty minimal effect. Their normal lifespan (no interference from drugs) is about four years. It will take at least two years for the Heartgard to kill them, maybe longer. So, it shortens their lifespan, but it sure isn't dramatic.

In the meantime, if you have a small number of adult worms present, they are unlikely to cause much heart damage. If the dog is athletic and vigorous, these worms (even in small numbers) get whipped around on the inside of the pulmonary arteries. This is not so great, and does damage them. If the dog is a couch potato, this effect is minimal.

When you treat the dog with Immiticide, you know that the worms will be dying in the next few days. You know that you need to restrict the dog's activity for the next few weeks. You know that you need to be watchful for the bad effects of the worms dying, shifting position and breaking up and clogging up arteries (coughing, difficulty breathing, fever, loss of appetite, coughing up even a drop of blood, or just generally not feeling good).

When the worms die "sometime in the next two or three years", you will NOT know when it is coming. You will NOT be restricting the dog's activity during that crucial time. You will NOT be alert and watchful for signs of the worms' demise.

If the dogs are ancient couch potatoes who do little and don't have much time left to do it in, yeah, I'd go with the Heartgard. If there just is no money to treat the dogs with Immiticide, by all means DO put them on the Heartgard.

If the dogs are young and active, get them cleared out with the Immiticide.

That's my take on it, speaking in broad, general terms. As far as advising you on a particular dog, you really need to talk to a veterinarian who can evaluate the dog in person. Internet advice is often worth what it costs.

Thanks for reading and writing.

Michelle S

I have a 5 yo Blue Heeler who has had his first injection of immeticide three weeks ago. He has had no problems so far. I am keeping him in a horse stall with a fan as he is a nervous wreck in the house. And with the stall, I do not need to walk him (he wants to trot even on the shortest leash), I simply clean his stall 2X daily while he eats just like the horses. The second doses will be given next week and he will be required to stay overnight. I was wondering if there is a time when he is in the most danger of having complications. If so I would like to put a crate in the stall to confine him even more. I did not think of this for the first injection. Also will he be in greater danger with the second dose or the first. Just would like to know what to expect and when I should try to be home to watch him the most. Thanks in advance.


Hello, Michelle,

Statistically, the single dose of Immiticide kills about one-third of the worms present: the weakest ones. The two-dose, two-day treatment kills 91% of the worms whether you give a preliminary dose or not. The combination of the full three doses kills 98% of worms (all of them, we hope, most of the time).

The biggest chance of a reaction is when the worms die and shift position, three to five days after treatment. This can be worse with the single injection, or it can be worse after the two-injection phase of treatment. This is not predictable. It just depends on how many worms there are and when they die.

I would not crate him unless he is showing signs of distress: lots of coughing, difficult breathing, coughing up blood, high temperature, not eating. Confinement in the stall should be adequate otherwise. You are trying to avoid aerobic exercise, the kind that elevates heart rate and blood pressure.

Thanks for reading and writing.


Hi Doc,

We rescued our manchester terrier mix, Hannah, a couple of months ago. She tested positive for heartworms. The vet put her on antibiotics to kill the organism that I guess lives symbiotically with the female worms. That was a 30-day course. Then she went in on Oct. 20th for her first injection. She was super healthy to begin with because I beefed her up with a healthy diet and colostrum supplements the month before the actual injection. So far she has not shown any adverse effects from the initial immiticide injection. No pain, and only one short coughing fit, but I think that was because she drank water too fast. We have not been walking her at all and I have been doing my best to keep her still. She is not a particularly hyper dog, but every once in a while she does get excited. Of course that nearly gives me a heart attack. She is mostly very calm, likes to ride in the car, and REALLY misses her walks. The vet has her on a staggered dosage of prednisone which she will finish up next week. It seems to stress her out more when she is crated, so we leave her out in the house if we have to be gone. She has a doggy door and our backyard has a built in dog run, so I can close off the rest of the yard to her and she can only roam a short distance from her dog door. She has to go in on Nov. 20th for a second round of shots followed by another month of quiet. I guess my question is this: Can she go on very short walks on leash? She acts like she feels fine, but I don't want to do ANYTHING to jeopardize her successful recovery.


Oops. Might help you to know that Hannah is app. 2 yrs. old and 30 lbs.


Hello, Jennie,

You should feel free to share your concerns with the doctor who is treating your dog, as he/she is best equipped to address your specific case. The course of treatment you have described is very thorough and indicates to me that your doctor is doing a great job.

Generally speaking, walks on the leash are okay. What we are trying to avoid is hard-charging, aerobic exercise. We don't want increased blood pressure that pushes the chunks of dead worm tighter into the smaller arteries. We also don't want increased blood pressure blowing out a damaged artery.

SO, if we walk calmly at heel, that's great. If the dog is acting like a nut, cartwheeling through her collar, and doing the power-pull against the leash, then that's not so great. Just walking isn't going to raise the heart-rate and blood-pressure. Acting like a nut (even if it's not just an act) is going to increase the risk of problems.

You just have to evaluate the dog's behavior in the circumstances to make the best decision (as when you elected to un-crate her in the home).

Thanks for reading and writing.


Thank you! I believe we do have a good vet, but getting this kind of real information has been like pulling teeth.

She does walk calmly and was so wiggly happy when she saw us putting on our "walking shoes" again!

Thanks for the good specifics. I feel less out to sea about this now.


My heart goes out to everyone who's pet has heartworm disease. On June 11, 2008 my husband and I rescued a 3 yr old Eskie. He was surrendered to a NY shelter than placed with an Eskie rescue organization. He was posted on Petfinders as healthy and UTD (up to date) on vaccines, altered and microchipped. I believe the chip shoud be decided by the adopter but, that is another story. Upon the first visit to my vet with "Snowy" he tested positive for HW. Immediately we started the proper treatment plan. Snowy did not feel very well from the injections and threw up his water for the first few days. He felt better as the weeks went on only to go through the misery of the next injection. He had a total of three injections along with medications. He had a severe case of HW. When the treatments were done I continued to bring him to the vet for evaluations. For the next three months he was feeling good and behaving like a healthy dog should. I couldn't wait to have the "sixth month HW test" that is administered after treatment for an accurate result... to hear he is HW negative. On December 2nd Snowy started coughing and seemed to have labored breathing so I brought him to the vet. They checked his gums which were a pale, grayish pink... a bad sign of lack of oxygen. They took an x-ray and blood and put him on oxygen. The blood (still) showed HW positve. The x-ray showed an enlarged heart but his lungs were good. Because he needed round the clock oxygen we had to bring him to an emergency vet a half hour away. We got there and Snowy was put on oxygen. Without going into the details of the devestation we were going through... because this was just 13 days ago, we got home after leaving him at the emergency vet only to receive a phone call that he had passed away just 10 minutes after we left. To say we are heartbroken is the biggest understatement of my lifetime. I am not posting to ask a question but to inform everyone who reads this.... PLEASE do NOT take for granted that a pet posted as healthy and UTD on shots means they are also HW negative. Unfortunately, shelters and rescue organizations are not working together on this issue. It is crucial when enquiring about a pet that a HW test be administered. If you aren't able to handle the expense ($1,800.00 in our case) and the heartache of losing your precious pet, this will save you a lot of grief. I have been in the process of communicating all my concerns on this issue with both the NY shelter and the rescue organization from which Snowy came. This is a serious disease that effects every state in the country because mosquitos are everywhere. Granted, it's worse in the southern states but not to be taken lightly in the northern states. HW prevention should be given year round with no breaks in between whatsover. I pray every precious pet on this website that is going through HW treatments comes through it successfully. We were blessed with our beloved Snowy for only six short months. I only rescue dogs but would be just as cautious with breeders and other sources of acquiring dogs.
Heartbroken in NH


Hello, Lynn,

I am sorry for your loss. This is always the kicker when someone adopts that dog who needs a home. Most other common problems are easily treatable with minimal expense.

It just kills me when someone is trying to "do the right thing" and find that they have adopted this major medical problem.

Fortunately, most folks have good results, but even so, it is still a big investment of time, money, and worry.

Best wishes.


Thank you for your response and sympathy. If just one person is helped through our unfortunate circumstance, and is spared the heartache, it is worth it for me to share how important it is to make sure of the status of the HW results before acquiring a pet.


Wow. I stumbled on Dr. Mobley's blog/site while being one of those "bad" foster parents Googling for heartworm treatment information. Our beautiful, 7-yr.-old rescue GSD, call sign "Turk," just had his first injection of Immiticide today after a month of Doxycycline, prednisone, & blood draws to ensure his platelets were w/in range first. Our heart also goes out to Lynne & her family re. Eskie. We were told by the Florida Keys SPCA that Turk was strong heartworm positive and they'd cover his treatment, and we may adopt him when he's medically clear. He is a dream dog. Well trained, loving, responsive, and, needless to say, we adore him. He is a little restless today, trying to find a space/place to get comfortable, but seems A-o.k. so far. We'll watch him closely in the upcoming week and beyond. Back to my point, in all the posts/responses, what calm, collected, compassionate wisdom. I can tell animals in your care, Dr. Mobley, are lucky, indeed. Thank you for giving of your time to help. All the way from Paradise (a.k.a. Key West), Suzanne (& Turk)


As seems to be the common story here, we adopted a wonderful 2 year old Scotty mix 2 weeks ago. Discovered 4 days after bringing her home she had Class II heartworm disease, no anemia, liver enzymes slightly elevated, very mild enlargement of arteries. Otherwise healthy and a real sweetheart. She had her 2 injections last Tuesday & Wednesday and has been having a very rough time of it. Heartworm is not common in our area, so no one seems to have any real definitive answers for me. She had back pain for a couple days and I suspect by her walk it is still tender. She began coughing on Saturday and had some wheezing, then more coughing and retching with a fever on Sunday. After an emergency visit to an on call vet we got anti inflammatorys that helped with fever and she rallied some. Yesterday we again had a lot of coughing with some panting and gagging. This has been accepted by the area vets as just the way it goes. In the night she coughed up 3 small pools of saliva/mucus/blood. She has not been interested in her dry food but will eat canned food and is still drinking water. After calling the vet this morning, they suggested bringing her in and starting her on a course of steroids. My husband felt that she was better this afternoon - more alert, less labored breathing, less coughing, no more blood and cancelled the appointment. Here is my question (finally!)...how bad is bad with the post treatment reaction? There have been a couple times when she has acted so sick I have wondered if she would live. She is confined and only going out on a leash to go potty - otherwise crated or in a small room on her pillow. She is not a hyper dog and spends most her time just laying there since treatment. Is this just the way of it and hopefully it will be over soon? Should I override my husband and take her back to the vet for steroids? How long do these severe symptoms go on and are they "normal" given the treatment? No one seems to know much here, so I am hoping you can advise.


Hello, Sue,

I don't know what part of the country you are in, but it does sound like they don't do a lot of heartworm treatments.

Corticosteroids are THE treatment of choice for heartworm complications. We would have started them at the first sign of difficulty. Waiting until the dog is having so much trouble worsens the prognosis. You should get the dog and and get treatment started as soon as possible.

There is always going to be some inflammation present in the pulmonary arteries as the worms shift position and break up. Even when the dog looks okay outwardly (and your dog DOES NOT), inflammation is taking place. For this reason, many doctors are now starting anti-inflammatory doses of prednisone routinely when the dog goes home, tapering the dose slowly over the next four weeks.

Whenever the dog shows any significant signs of difficulty (and your dog certainly is) we want to start steroid treatment ASAP.

Complications that are minor to start with can progressively become worse and the steroids can often prevent that.

The back soreness you observed initially was most likely due to the injections themselves. Even when severe, this is usually very temporary, 2 or 3 days at most. The problems you are seeing now are most likely related to the inflammation in the pulmonary arteries due to the dead worms. This makes the arteries swell shut, restricting flow, increasing pressure, back-pressure against the right heart, oozing fluid into the lungs, and possibly rupturing an artery.

In addition to the steroids, strictly restricted activity (cage rest) is important, and it's great that you are doing that.

I really cannot prescribe for your dog as I can neither see nor examine it. However, I strongly recommend that you get her back in to your veterinarian for treatment. Even if she seems a little better today, she will still benefit greatly from the medication.

The length of complications varies, but it takes the body several weeks to dissolve away the dead worms, so you are far from out of the woods.

Please take your dog back for evaluation and treatment.

Good luck.

Fawn Richter

I have enjoyed reading your thoughful responses to so many questions. here is mine asked with much respect.
What are your thoughts on the "slow kill" method? A rescue I foster for recommends Doxy for a month (although I found a study that suggests 2w is better) then Ivermectin every 2w for up to a year until a neg result is met. The reasons are primarily to make the tx less harsh and of course financial.
My second question is what HW tx is recommended for a lethal white HW+ Aussie. I believe they are in the Collie family and cannot have Ivermectin, right?


Hello, Fawn,

The doxycycline is intended to kill a microorganism called Wohlbachia that infests the heartworm itself. Many researchers believe that a great deal of the reaction we see to the breakup of the dead worms is related to the presence of this organism. This is not a universally adopted practice, but is inexpensive and does no harm (unless the delay allows more heart and artery disease to develop in dogs who have clinical signs of disease, versus just a "positive blood test").

Even when the Wohlbachia is gone, you still have chunks of dead worm to deal with, and they WILL cause inflammation in the pulmonary arteries. The inflammation causes swelling of the blood vessel, which restricts its inner opening. This makes circulation in the lung tissue poor, and increases the pressure on the compromised artery, and increases the back-pressure the heart must pump against.

This brings us to your question about using long-term ivermectin to kill the worms, and whether this is somehow "less harsh". Dead worms are dead worms, no matter what kills them. When they die and drift downstream, it doesn't matter what drug killed them or how long it took. They will still lodge and plug things up and cause inflammation.

With the dramatic increase in the number of dogs who get small numbers of heartworms despite taking monthly ivermectin (Heartgard 30, etc.) I have serious doubts that taking ivermectin every two weeks is going to kill the heartworms. Previous studies documenting this noted that it took as long as two years for the worms to die with this treatment (they would die of old age in about four years). These studies were made before we began to see the apparent failure of the drug to prevent heartworms 100% (in the past 3 years). Since they are getting new worms, it's hard for me to have confidence in the drug getting rid of the old ones.

Even if we accept that giving ivermectin twice monthly would eventually kill the heartworms (and I am not confident of this), we have to ask if this is really a good thing. When we give the standard treatment of the Immiticide injections, we know that the worms will die within the next few days. Thus we are alert for signs of complications. We also are now giving the dogs prednisone after their treatment in order to minimize the inflammation experienced when the dead worms move.

The bottom line is that we know when the worms will be dying and moving, so we can be on the alert and detect complications rapidly, and deal with them. We know that the dog's activity should be restricted while the dead worms are clogging up the works, and we can do this for the next five or six weeks.

If the worms were going to die at some unspecified time in the indefinite future, how in the dickens are you going to be on constant "red alert" for the next two years? Are you going to crate the dog for two years? Give him prednisone for two years? I submit that you will not be doing any of these things. Therefore, when the worms DO die, you are more likely to experience complications.

Since complications are related to how many dead worms are breaking up and hitting the smaller pulmonary arteries, it would make sense that the dog would do better if the worms died one at a time over a long period of time. There is NO evidence to say that this is what happens with the ivermectin (if indeed, anything is happening with the ivermectin). Even if you could prove that "in six months, the worms began to die one at a time, regular as clockwork, one-tenth of the worms per month for ten months" (and this is absurd), would you crate the dog for ten months, starting six months from now?

The sad fact of the business is that the Immiticide treatment is the only thing that we know is effective. We can reduce the risk by giving a half-treatment, and then waiting a month to give the full treatment. This also makes it more likely that ALL of the worms will be killed. (Unfortunately, there is no such thing as 100%, "always" or "never" when we're talking about this).

This (Immiticide treatment) would be the appropriate treatment for the Aussie. While they cannot tolerate high doses of ivermectin, they tolerate the preventive dose in Heartgard 30. You could certainly use Interceptor as your preventive instead, but it's not going to be effective in ridding the dog of adult heartworms.

It is certainly cheaper to give Ivermectin twice monthly for years than to do the Immiticide treatment. On the other hand, giving nothing is even cheaper. Doesn't work, but it's cheap.

Sorry that I don't have a quick fix for you.

Thanks for reading and writing.


My 3 yr. old rottie is vommitting. Mostly whole food. He is on Doxy and heartgard as its all we could afford. That alone hurt us some as we werent expecting it.

He always choked up clear water I dint think much off it he drools more than that. And I know its common for dogs to drink or eat too fast and do that. Every know and then a lose food would come out but no big deal. Latly its getting worse and real food not just water from drinking to fast or food caught in the throat.

Theres been no bile or green just his partial digested food. I know both drugs have vomiting side effects. Do you think its a side effect or just eating too fast or gutter gut. Tonight he puked 3-4 times and it really worried me.

Before it was once if it was mostly just a hack thing and maybe water somteimes a little food mixed in. It usualy happens after feeding a couple of hours in. Never in the middle of day or night.

But tonight after feeding it was bad. I thought he just got in to somthing on his walk as he does. He did get somthing in his eyes.

He knew he was going to get sick too which was strange usualy it kind of surprises him or he runs off the carpet this time he wanted OUT and Pets! He was trying to warn us we just didnt pick up on it.

I Started looking and found the side effects. If it is the doxycycline any suggestion on another. On the 15th of may we give him second dose of heartgard if that helps. He didnt seem to mind that. I dont know. We are just so short on money any advice would be helpful.

Lucky we dont worry about activity, this is the laziest dog I've known. Happy all the time greets everyone, plays, but lazy. 160 pound lap dog.

Smart too, shook his head no when I ask if he was OK. Nodes yes when I ask him if he needs go out. I didnt know you could train a dog do that. Too bad it was too late at the time. Always listen to your dog.


Hello, E.C.,

I'm answering your question as best I can with the limited information that I have. Your veterinarian (who has actually seen your dog) is the best person to advise you. I am assuming that the vomiting didn't start until after you started the doxycycline.

Doxycycline causes nausea in a lot of individuals if you take it on an empty stomach. Sometimes it makes me, personally, nauseated even when I do take it after a meal (I have taken it after tick exposure and getting sick). You want a good drink of water afterwards, too, to be sure a capsule isn't sticking in his esophagus halfway down. That can cause really severe inflammation.

If you are waiting until after a meal to give the doxy, and he has trouble anyway, we might look at an acid-reducer. Some dogs will benefit from famotidine. This is the active ingredient in Pepsid-AC. Over-the-counter Pepsid-AC is a 10mg tablet. A 160 pound dog would need to take four of these once or twice daily.

The purpose of the doxycycline is to kill Wohlbachia, a micro-organism that is necessary for the heartworm to thrive. If the Wohlbachia are killed, the microfilariae (the baby heartworms) die, and the adult heartworms shrink in size. When you stop the doxy, they will recover. The idea is to shrink things down and then do the Immiticide treatment. You should then have less reaction to the break-up of the dead worms.

If your dog has clinical signs of heartworm disease (lung problems, coughing, poor exercise tolerance, etc.), you may see a little improvement with the doxycycline. It is considered safe to give the Heartgard-30 (Ivermectin) to keep from getting any more worms than you already have.

Some dogs with heartworms don't have a lot of heart damage yet, but they have a lot of problems with inflamed arteries in their lungs. These dogs often show dramatic (if temporary) improvement when treated with prednisone (a form of cortisone).

Again, I urge you to contact your veterinarian with your concerns. Many times we send home medication, believing that we have explained things well, when people actually have a lot of un-answered questions. If we don't get a call back, we assume things are going well. Give your doctor a chance to help you.

Good luck.


Hi there. I wanted everyone out there to hear my short story about Lucky- my 2 year old pit rescue. He is a very healthy boy who has outrun the healthiest shepards and other dogs at the dog park. his energy is amazing. April 20 he was diagnosed with heartworms a mid level amount. I have had him and my other dog on Sentinel since I got him a year ago. He was in foster care for 3 months prior to that with a negative HW test. Prior to that he was at a pound for 3 months. So my vet believes he got it before I had him- but here I am 766.$ later. I love- no, obsess over my dogs so I naturally worried when I was told no outings, walks or playing with his sister.2 months confinement. So my vet does the injection in a dosing like this: first shot- 2 wks later a checkup, then 2 weeks after that a 2nd injection with a 3rd 24 hours after. He gave Deramaxx to me to give an hour before each injection for pain.Lucky did well with the injection as it was 3 ccs each time but not with a gimormous long needle as most use- maybe 2 inches long..I had so many questions and couldnt find enough consistent information on the web- so thought my post will help others. He panted and trembled and drooled for a few hours after each injection. The hardest part is keeping him from playing. He has actually gained a pound in one month (as we just had the last injection yesterday). I encourage buying dog treats and chew bones!!! These keep him occupied in the crate. There are also interactive toys for dogs (just google those words). I love them. If your dog is not a chewer- keep ice chips or cubes in a bowl in the crate.It also helps him to keep hydrated.I am a police officer and work alot so when I am home Lucky is not in the crate but we lay around together (Ive gained 4 pounds in the last MONTH )and when I do need to be mobile- I put his leash on and tie it to my waist so I can keep him from springing off to run around the house.Oh and a Kong full of pnut butter will keep him quiet too!If anyone out there has questions feel free to email me and I can try to help. Good Luck!


Hello, Kasey,

A 20-gauge, 1.5 inch needle is standard for the injection in larger dogs. You want it deep in the loin muscle (epaxial muscle). This muscle has no internal partitions of connective tissue, and the experts say that injecting here is "almost the same" as giving it intravenously. However, many dogs do experience soreness at the injection site.

If one is giving cortisone for the inflammation that occurs with the death and break-up of the worms, you don't want to give that along with NSAIDs, such as Deramaxx or Rimadyl. If no cortisone, then the NSAIDs should be fine.

Since we are giving cortisone for the inflammation (dexamethasone injections, followed by prednisone tablets at home), if a dog still has problems, we will give Tylenol for additional relief, sometimes even Tylenol+Codeine.

Even dogs that are REALLY sore tend to be fine in two or three days.

The panting and drooling are related to the pain and some temporary nausea. These are by no means an universal experience. We keep many dogs overnight and the majority do not display these signs.

In re "no playing", what you want to avoid is increased heart rate and blood pressure. This means different things with different dogs. If a dog is pretty laid-back, there's no reason not to let him go all over the house, and out for walks on a leash. If he's a hard charger, things are more difficult. We obviously don't want a prolonged run, but even short bursts of heavy activity can be a problem with a weakened pulmonary artery.

Thanks for reading and writing.


I have a 4 yr old terrier mix who was rescued in Texas. He's been with me in NY for 7 months. Only recently have I been able to take him to the vet since i'm unemployed, i just received my tax refund. He went in for tick removal and his first set of shots (rabies, distemper). To my dismay, they told me he tested positive for HW. He's my sidekick, my buddy. He's been behaving normally, healthy, loving, happy, protective... how a dog should behave. I have 2 cats that he tolerates and become his default playmates when he's bored. He's due to go in for his first HW treatment on Tuesday morning (6/2) and planned to stay overnight. Now, he's become my very close companion... by that i mean he's by my side all of the time. He sleeps with me, sits with me, goes on car rides with me. I fear that the overnight stay will stress him out. OR that when he arrives home, his protective nature will doom him to a clogged artery when he gets excited and barks at pedestrians from my bedroom window or when a tenant enters the building. When we go for walks, he jumps up and down from happiness to go outside. He can be a couch potato but he has his moments of outbursts. After reading the various posts i'm almost thinking that perhaps he's happiest NOW than with treatment. I can't afford this treatment but i will not hesitate to use every last penny to care for him and my cats. Part of my stress is also because i don't currently have an income, i'm afraid of complications that i won't be able to afford - NOW that really breaks my heart. I've contacted a society who will assist with vet bills, but it's not guaranteed that they will help. I still haven't heard back. I'm quite distraught.


Hello, Sam,

I hear your concerns.

While a night away from home is stressful, it is unlikely to have any significant effect on the heartworm treatment process. The worms do not die and shift position until several days after the treatment. This is when you need to be alert for coughing, fever, difficult breathing, loss of appetite, coughing up phlegm (possibly with flecks of blood), or just generally feeling bad.

If you notice a sudden change in your dog's behavior and the way he feels, you need to let your veterinarian know as soon as possible.

As far as his sudden bursts of activity causing problems during the convalescent period, it is certainly true that we want to minimize this. However, it is neither possible nor desirable for the dog to lie still for 6 weeks. You just need to look at the way your buddy views life, and arrange things to keep the craziness at a minimum.

Short bursts of activity can cause a problem, but are not as dangerous as prolonged aerobic exercise. Therefore, no running loose, no playing frisbee, etc.

There is always a chance that complications could develop, but this is true if you leave the worms untreated, as well. The odds are that you will be adding years to your buddy's life.

Good luck.



My 8 year lab recently tested positive for heart worms. I have been faithful with the Heartguard and can't imagine how this happened. My vet said that our region (Mississippi Delta region of Arkansas) has seen an increase in cases of heart worms even when preventative treatment is clearly been done.

Is he blowing smoke or is there some evidence to suggest that heart worms may be developing some resistance?

He said the test was at the lower end of the scale and that treatment should be successful, but I am seriously frustrated. If the once monthly doesn't prevent them even when given timely and properly, what possible options are there. I don't like putting her through heavy dose treatments, although I like heart worms even less.

She is a working dog and will miss duck season due to this. It will be harder for her than me I think (she loves it).

What is the deal with heartworms now?

Thanks in advance for your input.


Hello, John,

Starting in 2006, I began seeing a dramatic increase in the number of dogs who were supposedly taking preventive medicine year-round, yet were still coming up with a positive blood test. This has continued in 07,08 and 09.
I don't think you veterinarian is "blowing smoke".

My experience in treating these dogs to clear them of adult worms suggests that they have very few worms. In other words, the preventive prevented most of the heartworm development (from mosquito exposure), but not 100%.

I covered this in as much detail as I know how in a six part series last spring. I also cover more on the heartworm treatment process. Here is the link to the first of those posts:


In regards to missing duck season, there are two viewpoints here.

Number ONE: If the dog has very few worms, then it probably won't slow her down and she can hunt normally, being treated for the worms after the hunting season.

Number TWO: If a dog is really athletic and active, then even a few worms cause more damage to the pulmonary arteries. The increased heart rate and blood pressure really whip the worms around and could cause significant damage.

So THERE'S a difficult judgment call for you. If you want to play it as safe as possible, you treat her now. If you want to hunt, you treat her later.

I'm not sure when duck season starts, but if you treat the dog now, most of them are ready to rock by six weeks after treatment. I would suggest that you speak with your veterinarian about the time table.

As far as the medication that is used, that really almost never causes the dog a problem. It's the breakup of the dead worms that you're worried about.

Read through that series of six articles and I hope that you will have a lot of your questions answered.

Good luck.


We got a rescued 8 yr.old Pomeranian. When we took her for her shots & checkup she tested positive for heartworms. Our Vet said her x-rays & labwork showed the damage was not too severe. Our Vet said he has had better results with 1 shot & then 2 in a month. She had her first shot & it has been 2 weeks. She is eating good, drinking water & lets us know when she has to go potty. But several times a day, at night & in the early morning, she lays on the sofa & just trembles & her breathing is a somewhat labored & I can tell she is feeling very bad. Then after a while she perks up & seems to feel pretty good until the next bad spell. Is this normal for her to have these bad spells around the same time every day? When should this begin to subside? Thanks for reading..we have just never gone thru this & have completely fallen in love with her. She had been named Miss Angel & she is that & more.

Katelyn Johnson

My rescue dog had his first injection Dec. 19. Prior to that he was on doxycycline for one month. Jan 26 and 27 he had two more injections. Now one week after the final injections he has a fever 103.9 and a slight cough. He coughed up a small amount of blood. We took him to the vet and he received and antiboitic injection and 10 days of doxycline. He has not been exercised and has stayed as quiet as he has allowed us to keep him (he's a bit hyperactive). The vet said his heart and lungs sounded good. Are these normal side affects or could this be life threatening? Anything else we can do? Thank you for such an imformative article.


Hello, Katelyn,

This isn't "normal", but it is certainly a common occurrence as the worms shift position and break up. This is usually the worst time in the treatment period, so if he gets through this, the prognosis is pretty good.

If he is coughing a lot and coughing up blood, I would be thinking cage rest. I'd keep him as quiet as humanly possible for the next few days. Walk on leash only as long as needed to eliminate, and keep strictly confined the rest of the time.

If I were treating the dog, he would also be on some form of cortisone to reduce the inflammation in the pulmonary arteries, opening their diameter and allowing for more flow of blood, therefore reducing the pressure and the risk of more bleeding. The Doxycycline does have some anti-inflammatory activity, independent of its effect on the Wohlbachia organism (the heartworm symbiote).

The cage confinement would be the point I'd stress at the moment. Physical exertion could definitely increase the likelihood of a severe hemorrhage in the lungs.

Good luck, and keep your veterinarian informed as to the dog's progress.

Lori Jobmann

Our dog just head her second and third heartworm treatment. The vet injected her on Monday, then the third shot on Tuesday. We picked her up today. She has been fine, but when I took her out to eliminate, she had very watery light brown then bloody diarrhea. Is this to be expected?

Lori Jobmann

I forgot to mention, our dog, Talulah, is a two year old, 59 pound Louisiana Catahoula Leopard dog. She's otherwise very healthy. And her first immiticide injection was a month ago, and she seemed to do just fine...ie. no diarrhea at all. Thank you so much for your help!


Hello Lori,

The diarrhea is NOT an expected side effect. It is possible that your dog is just stressed out, and will clear up with symptomatic therapy, such as Pepto Bismol.

However, you should really let your veterinarian know about this, as it is not something we expect or typically experience. He/she will want to know and to stay in touch with you.

Good luck.


I just brought my sheltland sheepdog home from his heartworm treatment. Other than the most obvious (coughing,wheezing, fever, vomitting, and "feeling bad") what signs of distress should I be watching for? Should we be checking color of gums (my brother suggested this but what am I looking for??) or anything of that nature? This is still only the second day of treatment, I just want to be prepared for anything. Thanks very much.


Hello, Barb,

Most dogs have their greatest risk of complications when the worms die and shift position in the pulmonary arteries. This is usually 4 or 5 days after the treatment. It can happen sooner, it can happen weeks later. We keep the patient's activity restricted so that any running and heavy exercise is avoided as much as possible.

I ask my clients to look for coughing, difficult or heavy breathing, loss of appetite, fever (if he doesn't seem to feel well, rectal temp is normally 101.5, so anything over 103), coughing up any blood (even if it's mostly phlegm with just a drop of blood), and "just not feeling good".

Sometimes the dog is still eating, not coughing, etc., but you know your dog, and you can tell he does not feel well. You should contact your veterinarian when this occurs.

If he seems mostly okay and coughs once at 4:00 AM, you can wait until 8:00 to call. Don't wait two or three days, though, as the condition can worsen without treatment.

Good luck.


my dog just finished the last shot of the treatment last week she does not run jump or do any thing of that nature but she is coughing up blood what should i do


Hello, Chris,

If she is coughing up blood, you should confine her to as small an area as possible, like a cage. We don't want her moving around any more than is absolutely necessary. We want to keep her blood pressure from spiking and causing more bleeding, or blowing out where her body is trying to "patch" the leak. So, absolutely as little activity as possible.

If you haven't already done so, contact your veterinarian as soon as you can. He/she will want to get you on some anti-inflammatory doses of some type of cortisone as soon as possible.

Good luck.


Dear Doc,

My dog had his first shot of injection on 5/18, going for the second and third shots in two weeks on 6/21 & 6/22. He was doing fine since the shot (he had diaherra for about 3 days right after the first shot though). We still take him out for walk twice a day for him to do his business (he doesn't eliminate inside the apartment). He usually has light panting after a walk, but other than that he's just doing fine (no coughing, good appetite). However, as the weather has gotten hotter the past couple of weeks, he has been panting much faster due to the heat (even just relaxing at home). I want to know how should I deal with the heat, the walk, and also the complications from the up coming second and third shot of the injection, as I understand the last two injection will be much harsher? Thank you for your help and passion to animals.


Hello, Maggie,

Limit your dog's exercise. Make the walks as short as possible. Avoid the worst heat of the day.

The second go-round may kill more worms, or it may be about the same number. The first treatment of one injection of Immiticide usually kill the weaker worms, mostly males. If there are about the same number of females, the second round won't be any worse (probably). If more, it may be worse.

Be alert for coughing, shortness of breath, difficult breathing, coughing up even a drop of blood (even if coughing isn't bad otherwise), poor appetite, fever, or just generally feeling bad (even if no other signs are noticed).

If you see any of these things, let your veterinarian know as soon as possible.

Good luck.


Hey Doc,
I have a quick question about pain management. We just rescued a catahoula mix dog (about 1 yr) from the pound last month. He started the heartworm treatments right after. Today, we picked him after shots 2 and 3 of his heart worm regimen. He did fine with the first shot- just a bit of coughing and stiffness in back legs. My concern is our vet doesn't do the prednisone, cortisone or pain meds. Should I give him any OTC meds for pain? And if so, what kind? He seems a little stiff in his back area, but other than that- I can't tell that he is in much pain. What do you think? Thanks, Sharon


Hello, Sharon,

The soreness usually goes away in 2 or 3 days, even if severe.

A forty-pound dog can take one regular strength tylenol up to 3 times daily for a couple of days. Most will tolerate this without a problem.

No ibuprofen or naproxen (advil or aleve), as they can cause serious stomach problems, bleeding ulcers, etc.

Good luck.



I just wanted to make sure my stinky little buddy wasn't hurting too badly. I know the heart worm treatment is rough ..although I know the the worms dying and exiting is the worst part! Thank goodness we don't get them! Thanks again. Sharon


Hi- very informative site. Thanks so much for the info!

A little background: Last September we adopted what we and the vet have guessed is a jack russel/blue tick hound mix. She's appx. 2-3 years of age at this time and 35 lbs. She tested HW- at this shelter, which does a PHENOMENAL job with their dogs and treats for HW before adoption. We had to have our first dose of HW preventative IN HAND before we could even sign the adoption papers and take her home. She did have a suture reaction from her spay operation that required warm compresses to deal with a nasy lump and blister that formed, but other than that she was great when we got her home.

She's very laid back, very obedient, easily trainable, smart and sweet as can be. Will occasionally have a good burst of energy running around the yard with kids or after a cat, but not a real hi octane dog. It has pretty much been this way since meeting her at the shelter, which was a big draw for us as we are not overly energetic people.

I had noticed that she had what appeared to be allergy symptoms that did not go away during our first few months (bloodshot eyes, nasally sounding wheezing only when sleeping) so we changed her food to a fish based holistic formula and that seems to have improved. I did notice that she has stopped wanting to chase the ball as much as before, but I attributed that to the Memphis heat and also made a point to have her thyroid tested at her yearly visit. We had to stop our mile long walks because of the intolerable heat and humidity here during the summer months, so I am not sure how her actual activity tolerance is. She will also cough a really deep cough (only once or twice at a time, that sounds like she is coughing something up) a couple of times a week- but she eats anything she finds laying around, so I always assumed it was gagging because it was infrequent and not prolonged and she always looks at the ground whie doing so as if something is going to appear. In hindsight these might have been warning signs.

I took her for her yearly checkup where our vet did her first bloodwork since adoption. She seemed great on external exam, but the vet did warn me there was potential for her to come back HW+ because she is a rescue and of that window where they are infected but not showing up in bloodwork. I assumed that was rare and we left his office in good shape. I was truthfully more concerned about the thyroid coming back wonky.

Well, needless to say she came back HW+. I was in such shock that I did not get all the details on how advanced he suspects her case is or anything because this was Friday afternoon (it is Sunday night now). He was going to check with Novartis and see if they will help us with the treatment because she is a rescue and has been on their preventative meds for the last year. He said we would talk more early this coming week.

He did say that he felt nearly 100% cofident she would be fine with treatment, and that it should only cost us $300 to treat her. (He is a small town vet as well and does not push for services that are not necessary.) He said he had never lost a dog in his practice to heartworms because if he does not feel they have a good prognosis he will not put the dog and owner through the expense and physical/emotional toll of treatment.

From what I have read online this weekend, I am assuming he is planning to do the 2 dose method. He said she would need to stay one night at his practice, and that she would need to be kept calm for 30 days following treatment.

I am not certain if he routinely prescribes the antibiotic prior to the immiticide, but I intend to request that ahead of time if he does not usually do so. I am mainly concerned about serious complications from worm die-off. We are home most of the time (I homeschool) so supervision and restricted activity shouldn't be much of a problem provided she does not resist spending a lot more time in her crate. I was wondering how frequent the serious complications are and if we would be wise to get steroids in her system immediately after the immiticide treatment instead of waiting for a potential problem to develop. I have not known this vet for very long, so I don't want to question his treatment plan, but do want to do what is best for our sweet girl. I know he is not out to make a huge profit from the treatment since this cost is remarkably lower than most I have seen.

Also, we are right in the midst of the Mississippi river area where dogs who have proven record of being on heartworm preventative like clockwork are testing positive despite all responsible measures. ( This has happened to people we know, and several of their friends, as well as hearing the same from the shelter.)What should we do in the months to come to prevent re-infection if she does well through the coming treatment? Keeping her on her regular preventative is a given.

Any suggestions to maximize the chance we have a happy outcome? We have a lot of emotional investment in her and it would be really hard to lose her. However, we are not able to invest thousands of dollars into treatment either, so we are eager to do our best to prevent serious problems wherever possible.


Hello, Jennifer,

It sounds like you have adopted a great dog, and that you are developing a good relationship with your veterinarian.

I agree with you that the extreme heat makes it difficult to evaluate the change in the dog's exercise tolerance (I'm about 100 miles from Memphis, and it's been 100 degrees and high humidity for the last six weeks.)

Under the circumstances you describe, with a negative test last year, one would expect the dog to have only a small burden of adult heartworms. This is not guaranteed, and would depend on the level of mosquito exposure and the dog's individual resistance to the parasites.

If you want to "everything", then you could certainly ask for the doxycycline. Doxycycline inhibits Wohlbachia, a microbe that is beneficial to the heartworm.

Giving this medicine for 4 weeks prior to the Immiticide injections (to kill the heartworms) causes the worms to become weaker (thus more susceptible to being killed by the medicine) and acutally physically smaller (so less junk to clog up the blood vessels, and less for the white blood cells to have to clear out).

Treating the adult heartworms in two stages is considered to be safer than killing them all at once. If you have only a few worms, this would not be a big benefit. On the other hand, if you have a lot of worms, then killing half now and half later would be easier on the dog when the dead worms go downstream and lodge.

The two-stage treatment consists of giving only a single injection of Immiticide (which will kill the weaker worms), then four more weeks of doxycycline. When the body has gotten rid of the first batch, one gives the two injections, 24 hours apart, and this kills the rest of the worms.

Two injections given 24 hours apart will kill all of the worms in most dogs, but not all. This is true of the 3-injection, 2-stage protocol also.

Giving the corticosteroids (I use prednisone) immediately following the Immiticide is not a universal practice. However, since I heard Dr. Tom Nelson (past president of the American Heartworm Society) recommend it, I have thought that it makes sense. You know that inflammation will occur, so why wait until it gets bad enough to make the dog sick? (Which is what I did "forever" until three years ago.)

Now we give a strong anti-inflammatory dose of prednisone daily for the first seven days, then half that once daily for 7 days, then cotniue that lower dose once every 48 hours for 14 days. This has resulted in fewer night calls, because fewer dogs develop complications (that we can see). In fact very few dogs at all have developed outward complications.

Again, that is not "standard" across the profession, but I really think it is helping our patients.

Unfortunately, despite our best efforts, there are no guarantees. No matter what we do, sometimes a dead worm will lodge in such a way that a large vessel ruptures and the bleeding in the lungs is fatal. This is very rare, but it does happen.

Keeping the dogs vigorous physical activity at a minimum is an important part of the aftercare. Changes in your dog's attitude can reflect a problem coming on, so let your veterinarian know sooner, rather than later. Get the dog checked BEFORE it becomes an emergency.

Most complications are minor and treatable if they do occur.

Leaving the dog untreated is no solution, as the worms can cause a similar problem even if you have not yet treated the dog with Immiticide to kill them.

We treated a dog this week who was known to be heartworm positive. They had put postponed treating her. Sunday evening she had severe pulmonary hemorrhage, and coughed up a LOT of blood. She's on doxycycline and prednisone and cage rest now. I hope we will be successful in getting her through the whole process.

I hope that this information is helpful to you.


My little MaltiPoo just died three weeks after heartworm treatment with immiticide (first shot). She had been a rescue, and had tested strongly HW positive. She had been on doxycycline for a month prior to treatment and she seemed to feel fine. She had problems with breathing about a week after treatment, and she was kept for an additional two nights, put on steroids and oxygen. She came home on oral prednisone and had completed most of it when I could tell she began feeling really bad. I started to take her in but the vet was closing early that day and would be gone the next, so she would have been alone. I decided to keep her until the day after. The night before I was going to take her in, she collapsed in the yard when she went out to urinate. I took her to an emergency clinic, but she had died when we arrived. She had not been confined to a crate, but she was not an active dog and since she felt bad she had just been lying around except when she needed to go out. A post-mortem was done, and it showed an embolism, one dead worm and three dying. I keep turning this over and over in my mind because I feel responsible since she wasn't kept crated. How could this have happened? Why would she die when she was not active at all?


Hello, Ginny,

I am sorry for your loss.

Some dogs have a bad, allergic type reaction when the heartworms die. This is similar to when a person who is seriously allergic to bee-stings has a reaction. They just turn blue and fall over.

Unless you are standing right there with your epi-pen (epinephrine, aka adrenaline) it's too late to do anything by the time you travel anywhere.

This is quite rare, but I suspect it is what happened. It has nothing to do with whether the dog is crated or not. It is not your fault, and is impossible to predict.

Sometimes our best just isn't good enough, and that hurts.

Best wishes and thanks for reading and writing.

Jennifer Blake

Hi! This is Jennifer from a couple of posts up with the HW+ blue tick/jack russell mix. I am happy to report that today is day 32 since her treatment, and we have been cleared for activity by our vet (he said once Halloween was over she should be good to go.) She tolerated the confinement, treatment and recovery without a hitch and we couldn't be more pleased. We did the 2 shots 24 hours apart- our vet said that with all things considered he felt that was the best route. He could have done the other method with 1 shot then 2 more a month later, but if she were his particular pet he would do the treatment he did for Bella. He did do (when I asked about it) the doxy for 4 weeks prior and the prednisone for 2 weeks after. She only had one coughing/gagging episode about 2-3 weeks post treatment, and no other signs of discomfort at all. She has been energetic when on leash, eating just fine, content in her crate and an all around excellent patient. After I re-doggie proof the house today we are giving her free range inside, then I am going to give her a couple of more weeks on the leash in the yard just to play it safe.

She has had a couple of coughs/gags the last week- but I suspect they were related to grooming herself as she is a heavy shedder. She did not seem in distress or anything. I was curious though if your previous message with the maltipoo that died and still had large worms intact and dying 3 weeks post treatment was normal. It was my understanding they should all be dead and dissolved before the 4 week mark. Is 30 days the appropriate length of time to wait for exercise to resume?

Also, I understand the immiticide kills the adult HW, the monthly preventative (we use Interceptor) kills the microfiliare, but what kills the maturing worms if they are present? Is there another treatment step I need to ask about? Our HW preventative does not contain ivermectin.

Thanks so much for your site and your down to earth advice and information. It is refreshing to see that there are vets out there that want to keep their patients healthy without fleecing their owners.


Hello, Jennifer,

Most worms should be dead and dissolved by four to five weeks, but this is variable with the number of worms and the action of the dog's own defense system. Those microscopic white blood cells have to eat those foot-long worms. It can be a slow process.

I usually release my patients for exercise at 5 to 6 weeks post treatment.

Yes, Immiticide kills the adults, preventives kill the microfilariae. We do not have medication to kill the developing worms. Dogs who are treated in the fall might turn up positive the following spring, as microfilariae that were missed in the summer's preventive reach maturity six months later.

Sometimes we try to delay treatment until six months after mosquito exposure. Sometimes this is not in the dog's best interest, and we might have to treat twice. The rules are not hard and fast.

I'm sorry you feel that some veterinarians are "fleecing the owners". It costs a lot to keep a veterinary hospital running and ready for you, even if the doctor didn't get paid a dime. My own hospital overhead is $32K per month, excluding any compensation for me, and I'm in a small, low-income town, in a rural area.

I'm glad that your dog is doing well so far. It sounds like things are going to work out great.

Thanks for reading and writing.

Joanne Kutzler

I certainly hope other dogs and owners do not have to go thru what we have been thru. I have a wonderful 1 3/4 yr old Irish Setter/Coon Hound rescue from Kentucky. She tested negative for HW January 9, 2010 and was given the preventative Revolution. I adopted her in Feb in Minnesota and she was started on Heartgard by my vet March 1. She received her Heartgard tablets faithfully from me the 1st of every month for the last 9 months(last one given this Nov 1). She showed absolutely no signs of any fatigue, coughing, or breathing difficulties. On Nov 2 we made a run to an emergency vet at 2am when my dog seemed uncomfortable and lethargic. While at the hospital she thru up, broke out in hives (bumps all over her body), had whitish gums, and abnormal lack of blood clotting.
After much testing it was finally determined that she was HW positive.
She has managed the 2 Immiticide shots and is feeling much better now after two 1/2 weeks.
I do not understand how and why she got so ill so quickly and how she ended up HW positive. It was relatively easy to keep her inactive for the first 2 weeks since she really didn't feel very good but now she getting her energy back. Any suggestions for how to keep my "born to run" youngster "calm" for another 6+ weeks ????
Thank you very much for your wonderful website. Your thoughtful responses and expertise are greatly appreciated.


Hello, Joanne,

I can certainly appreciate your frustration. Things have in no way gone according to our expectations in such a case.

It is possible that your dog just has zilch resistance to the parasite - there are certainly dogs that do. I once had occasion to do a post-mortem on a dog that had moved from a mountainous area to our mosquito-infested area. He died at 18 months with a chest FULL of heartworms. Dogs that have been bred in this area would rarely see such a situation before 3 years, even with super-heavy exposure.

In re keeping your dog quiet, I do not like to keep patients sedated. However, I have done so a few times. You might consider getting one of the DAP (dog appeasing pheromone) diffusers to put in his area of confinement. This often makes dogs more contented.

Taking her for short walks on leash may help if she doesn't get too rambunctious. Another thing you might do to relieve boredom would be to get those Kong toys where you hide the treats inside. Making her really work for her food may help keep her mind occupied.

I'd also consider a lower-calorie, lower protein diet. No point feeding rocket fuel if you can't let the dog blast off.

Share your concerns with your veterinarian. In extreme cases, we have given sedatives for a couple of weeks or longer, though I do not like to.

Thanks for your kind words, and good luck.


We have a 3 year old beagle that we adopted March 2009. She just finished being treated for heartworm when we adopted her. Since then she has tested positive for heartworm and been treated twice more. She just had her HW test and tested positive again. Why does she keep testing positive after being treated 3 times? I forgot to mention that she has been given Heartgard every month.


Hello, Pam,

Has she had a full 3-dose protocol with Immiticide 3 times?

Is she testing positive for microfilariae (baby heartworms)?

Is she testing positive for adult worms (antigen test)?


If it is just the microfilariae, sometimes treating for one month with doxycycline will clear them.

There are certainly dogs where we have difficulty clearing the worms, but your situation sounds extreme.

With more information, I might be able to tell you more. DO continue the Heartgard. Did you start it when you first got her?

Jessica Meister

My boxer had his first of three injections for heartworm today. The vet and staff who we respect said he was doing fine and told us to look out for increased resp., coughing, and temp. When we got home I noticed his eyes where really red, which can happen with is allergies, but his gums are also very red. He is def. slower, like I'd expect after all the medication, but not completely lethargic. His skin temp feels normal, I'm not sure how to take a dog's temp and he isn't panting. We also didn't get sent home with any of the other medications people are writing about,(prednisone) or anything else. We don't have a 24 hr vet so I'm not sure what to do because I only get an answering machine after hours. Can this wait til the morning?


We just found out our dog is HW positive. High Risk.

We are taking him for treatment - two injections in 24 hours apart and four months of after care. One vet is 1300 for this treatment and a Low cost spay neuter clinic does this treatment for 350. Is the there any difference in treatment? I am worried about the cost (unemployed right now).


Hello, Angela,

I can understand your concerns. Without knowing what is covered by those fees, I really can't tell if you what the difference is.

There are the initial injections of Immiticide which kill the heartworms. When we treat the dog, our fee would also cover a month of prednisone to go home, recheck at 6 weeks (when the heartworms should be dead and mostly dissolved) and four months, and blood test to be sure they are all gone at four months.

We would also recheck the dog at no additional charge if there are signs of complications. There might be additional cost for other medicines, or if problems turn out to be unrelated to the heartworm treatment.

I do not know what each hospital is actually providing for you. The low-cost option might have additional costs later on. You would just have to ask what is covered.

Good luck.


Hello, Jessica,

The only way to take the temperature is with a thermometer, rectally. The average normal temperature for a dog is 101.5 degrees Fahrenheit. A degree above or below would not worry me.

Many dogs have pain and inflammation associated with the Immiticide injection. This is not really an emergency, but you need to let your veterinarian know about it.

Even when the soreness is severe, it generally does not last more than three days. Do not use over-the-counter pain relievers without consulting your dog's veterinarian. Many pills that are pretty safe for people can cause bleeding ulcers in dogs.

A cold compress on the injection site can help. The injections are given in the heavy muscle of the lower back, what some call the loin area.

Do call your veterinarian about this.

LaVera Potter

Glad to find you. I have been reading for days about heartworms looked at more pictures than i wanted to see. I have a seven year old standard poodle who has tested postive. I was going to have the standard treatment done but the more I read I was afraid. At the moment I are using the homeopathic method. I don't know if it works but we shall see. He is eating well,active, but seems so thin. I have even been cooking for him in addition to dog food to try and put some weight on. Thank you for being honest I feel better. I will have him retested at 9week mark of treatment. He is coming up on week three.


Hello, LaVera,

I fear that you will be disappointed in homeopathic treatment for the heartworms. Even Dr. Huisheng Xie, world famous holistic veterinarian, does not recommend this. Here is a website that gives you an introduction to him. http://www.tcvm.com/about/about_Meet.htm

Anything that kills the worms is going to result in dead worms moving downstream and clogging up blood vessels. Doesn't matter whether it's herbs, Immiticide, or space alien death rays. The dead worms are the problem, not the medicine.

While there were some doctors advocating that the dog simply be kept on preventive medicine and wait for the worms to die of old age (3 to 4 years), the American Heartworm Society no longer feels that this is in the dog's best interest. An exception would be an elderly dog with minimal physical activity and very few worms. He might live just as long without treatment as with it.

When you treat with Immiticide, you have a very close idea of when the worms will be dying, and you can be watching the dog closely during those days and weeks. With the "wait for natural causes" method, you would need to be restricting the dog's activity and taking great care to watch for complications for YEARS.

Our standard protocol now is to pre-treat with doxycycline for 4 weeks, which weakens the worms. It makes them easier to kill, and physically smaller, so less blockage problems. Then we give a single injection of Immiticide, which kills the weaker worms (statistically about half the dog's worm burden). The dog continues with doxycycline through the next four weeks (to keep the remaining worms weak), along with some cortisone to keep down inflammation in the pulmonary arteries.

After those first bunch of dead worms are dissolved (about four weeks), the dog is treated with Immiticide once daily for two days. This kills the rest of the worms. Again, we give some cortisone for the inflammation.

In six weeks, the dog gets a follow-up exam, and the dog is usually returned to normal activity. In four months a blood-test is done to be sure that the worms are gone.

Best wishes.


Great site, with lots of good information. I am getting conflicting information on the amount of "down time" a dog needs after hw treatment. Our foster, now forever family member, was treated for hw in November and the vet won't release her for even minimal training classes until June. Also she still coughs ever so often (like a hairball cough) is this hw related or just a random cough?


Hello, Leigh-Anne,

Your veterinarian has more familiarity with your particular dog than I possibly could, so it's difficult for me to make specific recommendations.

With dogs who have had low worm burdens and done well with treatment, we usually begin allowing gradual return to activity six weeks after the final Immiticide treatment.

That being said, there are dogs who seem fine, but who have had an artery weakened during this process. When they resume activity and blood pressure rises, the artery breaks, and bleeding into the lungs occurs. This is a quite rare occurrence, but it can surely happen.

The cough may be random, or there may be residual inflammation in the lungs. If a chest X-ray looks good, it is possible that a short round of corticosteroids could resolve that.

It would be best for you to discuss this at more length with your veterinarian, and share your concerns with him/her.

Best wishes.


my dog is going threw heart worm treatments why is he throwing up


Hello, Brandon,

You should call your veterinarian about this. Some dogs are nauseated when they take doxycycline, and it can help if you give it after a meal.

If he is not taking oral medications, then I cannot think of any heartworm treatment related problem that would make him throw up. That means something unusual is going on.

While most dogs have almost no reaction to the Immiticide injections (other than temporary soreness at the injection site), it is certainly possible that a dog could be really sensitive to it. I have never seen this, but some people cannot take even an aspirin. It is certainly possible that your dog might have had a problem with the Immiticide.

It is also possible that it is totally unrelated, i.e. he ate garbage, etc.

In either case, you need to let your veterinarian know what is going on. When he/she doesn't hear from you, they just assume that everything is going well. Let them know what is happening.

Good luck.

Cathy Hinchliffe

my dog, Zeus, was treated today for heartworms and is breathing very rapidly and hasn't stopped doing this since he has been home, I called the vet and she said to bring him in first thing in the morning because she was going home for the evening but he may have "thrown a worm" into his lungs. What does this mean? Is he going to die overnight? I don't know what to do.


Hello, Cathie,

In re: "throwing a worm" (lousy description)
The worms live in the larger diameter pulmonary arteries (that take blood from the right side of the heart to the lungs to get oxygen), pretty close to the heart. When they die, they flow downstream and plug (or partially plug) the smaller blood vessels. This can make the dog feel pretty bad.

The worms do not die for several days after the injections, but sometimes they can move downstream anyway. This can cause problems, as the lung downstream gets poor circulation, the artery is inflamed, there is more back-pressure against the heart's pumping action.

Another thing that could be happening is just pain from the injection site. The drug is pretty irritating, but dogs really have a variable response to this. There are dogs who have absolutely no discomfort, and others who are crying and you cannot touch their lower back without them screaming. In between you have dogs that are pretty painful, but not crying.

Fortunately, this almost always passes in a couple of days, even with the really bad ones. We routinely give prednisone (a type of cortisone) for the inflammation, and sometimes find it necessary to give a pain-killer like Tramadol short term.

Do not give over-the-counter pain relievers to your dog without consulting your veterinarian. Dogs have a much lower tolerance for things like Aleve and Ibuprofen. Bleeding ulcers can occur with a single dose.

Keep your veterinarian updated on the dog's condition. You can safely apply a cold compress to the lower back area where the injections were given. Keep the dog as quiet as possible until your veterinarian can recheck him. Most dogs get through the treatment with minimal complications. However, I know nothing about your dog's case and you need to consult with the veterinarian who does.

Good luck.


Hello Doc,

I stumbled across this site last week and practically read every word on this page, I wanted to feel prepared when my dog began her heartworm treatment. I must say that it really eased my mind and I was ready for the beginning of treatment.

We started my 9-yr old chow on treatment a day and a half ago (Thursday, April 20th). The vet opted for the shot, wait a month, then the two shots separated by 24 hours approach, she said it was the safest. So far there wasn't any problems at the injection site and she was happier than ever when we picked her up from the vet (I know she might get down a bit in a few days when the worms start to die so I'm waiting for that).

Anyways, my question is this. She's currently on the last bit of prednisone (9 half pills remaining, to be taken every other day), has 2 days left of cephalexin, and is taking something-flex for arthritis in her hind legs. She was given the pred. and ceph. after we took her to the vet for a skin and ear infection (finished ear drop treatment).

Trying not to ramble on here, the prednisone is making her eat and drink like no tomorrow. And obviously with eating comes elimination of the waste, which she has to do a lot of. She really likes to take her sweet time during a bathroom walk (on the leash, no more than 20-30 feet), sitting in the hot Florida sun/humidity. She'll pant for a tad and drink a lot of water after returning from outside. Other than that she is sedentary every second she's inside, shell get up to walk from room to room on occasion, that's it. It's just the fact that she cries to go out at such a large number now, sometimes 5-7 times a day. Unlike normal when it would be 2-3 times at most.

Is this going to be dangerous when the worms begin to die? I'm really worried. How much is too much? She doesn't jog nor run, but I'm worried if the 3-4 times a day she's exposed to the mid-day weather will really beat down on her. Am I worrying too much about this?

And one last thing, she has extremely bad gas, it clears rooms. Is that related to any of the meds/treatment?

Thank you for everything you're doing, it's greatly appreciated.


Hello, Doug,

The prednisone causes the dog to produce larger volumes of more dilute urine. When you get off the pred, the urination situation should return to normal.

As long as she is just walking and not distressed or struggling, the trips outside should be no problem. We only recommend cage confinement when a dog is having serious complications, like trouble breathing, or coughing up blood.

I doubt that the flatulence is related to the meds. Here's a link to a great article from VeterinaryPartner.com



Hello Doc-
First of all, thank you so much for the wealth of information you provide here! We adopted Max, a min pin mix, about 5 weeks ago off of the street. The vet said he is between 2-3 years old and he tested "faint" positive for heartworms and will be going in for his 2 shot/days treatment on June 13. Max is so very, very scared of storms. We live in Texas and our stormy season should be over now, but my biggest fear is that is we have a storm shortly after his treatment that it could cause major trouble. Max paces when the storms start and this lasts for about 30 mins or more, and he also shakes nonstop for the duration of the storm as well as some time post-storm. The Animal Rescue group doing his treatment (their cost is less than 1/3 of what our vet charges) said that we won't be able to give Max anything to help calm him down in the event of a storm post HW treatment because of the uncertainty of how a medication may react with the treatment. Should I be concerned about the stress it would cause him if we have a bad storm after he receives his treatment? If so, do you have any helpful tips of how to help Max without medication? Thank you again for providing this site with such great information.


Hello, Sarah,
I do not think that the thunderstorm anxiety will raise the dog's blood pressure enough to increase your risks in the convalescent period after the Immiticide injections (6 weeks).
I have not seen your dog, but generally I would not think a mild sedative would have any more adverse effect in this situation than otherwise.
There is a product called Composure, made by Vetri-Science, that you might try. It is not a drug but a combination of vitamins, amino acids, and mysterious substances (no kidding).
It is classified as a nutritional supplement, and comes in bite-sized treats. We have had several patients who do really well with this product. It hasn't helped my own dog's thunderstorm anxiety at all, but it has really helped a lot of our patients. It's not expensive, and would be worth a try.

Good luck.

Jan John

Thanks for so much information in so little space. I feel better about my dog's recovery now. She does cough (no blood) and is tired after a short walk, but I think now that that's the recovery at work and not a return to trouble with HW. You write 4 weeks and6 weeks after the second round of shots. I've been told 4 weeks is sufficient. Should I be thinking 6?


Hello, Jan John,

I used to cut it off at four weeks and occasionally had a dog who had a little trouble on returning to activity. It didn't happen often, but enough to bother me.

I stretched it to six weeks several years ago, and this rarely happens now.

Good luck.


I have a newly adopted heartworm positive shelter dog, 4 years old, Corgie/Chow Mix. He was ELISA Snap tested at first check-up because I wanted to put him on preventative. He was/is showing no clinical signs. We live in southern AZ. He did have X-rays that showed mild thoracic changes. He was also given a Desert Disease Panel to make sure he didn't have Valley Fever or Tick Fever, to better proceed with a plan of action. He did have slightly elevated globulin levels. We are doing three months of Interceptor preventative to kill microfilaria and give juvenile worms time to mature to adults before starting adulticide (3 injections) 1 1st month, followed by back to back days 2nd month. We are in month 2 of giving the preventative. He had a mild reaction (vomiting and increased respitory rate)after given Interceptor the first time. He was treated w/steroid injection and Benadryl. Second dose went fine, I gave him Benadryl 30-45 min. before the Interceptor, as recommended by vet. I ran across some info. that recommended a second test if the dog is not from a hypoendemic area. The X-rays showing a slightly enlarged heart could be congenital? Would you recommend a second test before proceeding w/ Adulticide? Also, could you explain a little about the effectiveness of the Snap Test in identifying positive cases, and explain "specificity" and "sensitivity"?

Thanks so much for giving your time to this blog.


Clarification: Would you recommend a second HW Snap Test in case the first one was a false positive?

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