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August 24, 2009


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I find this fascinating. That there are worms who target the heart, and not another organ. It's not a very good parasite, because it kills the host.

But, am I wrong in understanding that there is no cure for heartworms-just something that keeps more from developing? Hard to believe with all the advances in science, we can't find something that will kill a simple parasite while not harming the host.



The Immiticide DOES kill the heartworms and let you start fresh. This guy just didn't think he could spring for the cost. Here's a link to that discussion: http://www.yourpetsbestfriend.com/your_pets_best_friend/2009/05/are-heartworms-getting-worse-a-seminar-part-5-of-6.html

It's a great parasite, because it takes YEARS to kill the host. In the meantime, it reproduces by the zillions.

Thanks for reading and writing.


I'm just curious about the damage caused by frequent exercise. That seems just the opposite of what should happen with people, so am I completely misunderstanding what you're saying?


Hello, Margaret,

Excercise is beneficial in strengthening muscles, including the heart muscle. This is no different in dogs than in people.

Exercise increases heart rate, and increases blood pressure. In dogs who have foot-long worms in their pulmonary arteries, this creates problems. The more turbulent flow of blood whips the worms harder against the lining of the arteries, and may shove them down tighter into smaller arteries.

This causes inflammation, leading to swelling of the artery wall. This thickening of the artery wall then narrows the opening in the middle, restricting blood flow.

It is much more difficult for the heart to pump the same volume of blood per minute through a tiny opening than through a big opening. Thus the heart becomes overworked, and begins to deteriorate because of that.

I hope this clarifies things.

Thanks for reading and writing.


I just adopted a 2year old pit-bull and would like to start giving him preventatives for heart worms. After all that I have learned about these multiplying parasites. I will start giving him Heartguard soon. Thank you for the information. http://www.entirelypets.com/hearplusford.html

pulmonary disease

Chronic bronchitis involves inflammation and swelling of the lining of the airways that leads to narrowing and obstruction of the airways. The inflammation also stimulates production of mucous (sputum), which can cause further obstruction of the airways. Obstruction of the airways, especially with mucus, increases the likelihood of bacterial lung infections. Chronic bronchitis usually is defined clinically as a daily cough with production of sputum for three months, two years in a row. This definition was developed primarily for research so that like patients could be compared.


I adopted a 4-year German Shepherd/Cattle Dog mix that was heartworm positive (large load). That was back in July 2009. Since then, my dog was given the 3-shot Immiticide protocol: the first shot was administered in July; the last two shots were administed in October within a 24 hour period. Since November 2009, I give my dog Heartgard once a month. And in February 2010, I learned that my dog tested negative for heartworms.

Yesterday, I realized that I forgot to give my dog the March 1 dose for Heartgard. I gave my dog Heartgard as soon as I realized this, but I'm 23 days late.

Will my dog's heartworms come back as a result of my forgetfulness? I'm imagining that some heartworms survived the Immiticide treatment and have taken advantage of my lapse to come back full force.

Thank you in advance!


Hello, Mike,

The Heartgard dose has virtually no effect on adult heartworms. Your tested negative in February. If you were to get a positive test result in the near future, it would be from exposure that occurred at least six months previously.

The dose you are late on would only be pertinent to mosquito exposure in the previous five weeks. That was February, so unless you are in the southern hemisphere, you probably didn't have many mosquitoes in February.

Just get back on your regular schedule. You could start giving it on the 23rd from now on, but if the first of the month is what's easy to remember (as it is for most of us), then it won't hurt to give another dose on the first of April. The medicine is out of the dog's system in 24 to 48 hours, so you won't be giving some huge dose (and it wouldn't hurt if the dog DID get a double dose).

Don't sweat it. Just get back with the program.

Good luck.

BJ Jackson

I adore my dogs and try to take care of them, but they started battling taking any pills, even heartworm medicine. Since our immediate area has had a clean record for heartworms for several years, I decided the preventative was not essential. Last year I lost a wonder pomeranian to whip worms. I found out that Interceptor is a preventative for whip worns when one of my other dogs tested positive for heartworms. Our area is no longer clear. We learned a hard lesson, but the precious animals did not deserve to pay for our ignorance. We will begin the treatment in just over a week, and our semi-hyper, 15 pound dachsahuaha will have to be calm and still for 2 months.

cindy kuschel

I have been rescueing dogs for 20 yrs. I usually treat the hwm pos ones with the immeticide. However, lately I just can not afford it and 2 vets in the area say it is ok to just use the monthly heartgd and eventually they will test neg. How long does this usually take? My dtr's fd wants to adopt a positive dog as a jogging buddy. The pos dog has been on heartgd for 2/3 mos but is this safe?? Thanks - cindy.


Hello, Cindy,

It is safe to give Heartgard to the heartworm positive dogs. It can take two years or more for the dog to clear with just Heartgard. Sometimes it does not work.

In the last few years, we have been trouble with outside dogs getting new heartworm infections, despite taking monthly preventive medicine (whether Heartgard, Interceptor or Revolution). This gives me a lot less confidence in clearing adult worms with Heartgard. This has been a problem mostly in the Mississippi valley, rather than the rest of the country. It starts about 100 miles south of St.Louis and gets worse the farther south that you go.

The level of the dog's activity is very important in determining the amount of damage that heartworms do. They live in the pulmonary arteries, and heavy activity with rapid heart rate and higher blood pressure (aerobic exercise) whips them around the inside of the arteries.

It has been well documented that a "couch potato" with quite a few worms experiences less disease and damage than an athletic dog with a smaller number of worms.

Thus, a heartworm-positive dog as a jogging buddy is not an ideal situation. It would really be better to clear the dog of heartworms before starting strenuous exercise.

If there are very few worms (which is really not possible to quantitatively determine in the live dog), you would probably get by with it.

Someday, though, those worms will die, and float downstream and clog up an artery, and the dog will feel bad. It may not be serious, but then again it might be. This is what happens when you treat with Immiticide. Then, however, you are confining the dog and watching it closely, rather than jogging with it.

I hope this helps to answer your questions.

Good luck.

Deidre Darling

I read somewhere that if you're using the slow kill method, it has to be regular HeartGuard, not HeartGuard Plus. Do you know if that's true, and, if so, why?



Hello, Deidre,

That makes no sense at all. The only difference between the two products is that the Heartguard Plus has Pyrantel pamoate added to it. This drug kills hookworms and roundworms in the intestine. It is a very safe drug -- we use it do deworm 3-week old puppies and kittens.

Thanks for reading and writing.


3 days ago I rescued a choc. lab on its way to the pound... He is about 3yrs old and this MOST amazing dog in the world... Today, he tested positive for heart worms. The vet was not very clear on the severity of this case.. but was really wanting to push the fast treatment... He gave me Doxycycline AND Interceptor...in 3months we will start the round of shots... I guess all the research Im doing is making this situation stressful on what I should do..... about 50% articles I have read say DONOT give interceptor to Heartworm positive dogs.... what do you suggest...


Hello, Buckles family,

While the accepted standard is that Heartgard is safer than Interceptor when a dog has microfilariae (microscopic baby heartworms) present in his bloodstream, there are certainly dogs that have no problem with the Interceptor.

If your dog is only showing positive for the adult heartworm protein (an Antigen test or "occult" test), then the Interceptor should be okay.

Heartgard is supposed to be safer if there are babies in the blood.
Ask your veterinarian what the situation is and what his/her viewpoint is on this subject.

If the dog doesn't have any clinical signs of disease, it would be good to wait several months to treat. This is because he has been getting mosquito bites already this summer. The baby heartworms he acquired in the last 5 weeks should be killed by the Interceptor or Heartgard. The ones that were put in before that will be too far along to be killed by the preventive. They won't be susceptible to the Immiticide treatment until they are several months old.

If you were to treat the dog now, you might have a positive test in February, even if he shows completely clear in November. They you would need to treat again to clear the worms that developed from his exposure in May and early June.

Discuss your concerns with your veterinarian.

Good luck.


We live on a farm and it was recommended to me to start giving my dogs ivermectin, that it would take care of all internal parasites, I was told by my vet how much to give, all of my dogs seem to have no ill effects, except.. my doberman.. shortly after I gave her ivermectin (I would say about a week) she became lethargic and so pale as to be almost white, I began just treating the symptoms, i.e., chicken liver (cooked) to help with anemia, vit c to help with the absorbtion of iron and very limited activity. 2 weeks into I felt I was loosing her, took her to a different vet, he did bloodtests, exrays and physical exam all to the tune of $346.00 dollars, then came back and said I'm stumped, I don't know whats wrong, the blood tests came back normal except for only a minimal increase in pancreas enzymes. Meanwhile, 2 weeeks after that, she is still grossly pale, no energy at all.. her resting heart rate is very shallow and I'm out of money, so again I am back to battling just the symptoms. What I have read about heartworms is that when they die they can clog the arteries etc, all of which add up to her symptoms, anemia, shallow breathing etc.. my question.. have I killed my dog? she seemed perfectly fine before.. no outward symptoms of heartworms at all, and now this. I am heartbroken but want what is best for her, we are into this a month now and her quality of life is diminished to the point of heartbreaking, sorry for the novel but wanted to give you as much info as possible. your input will be much appreciated. she turned 6 09/10


Hello, Trish,

This doesn't sound like ivermectin toxicity. Your general description sounds like s dog who is really anemic, which the blood tests should have shown.

This is not typical of heartworm disease. Post-caval heartworm syndrome can make them super sick, super fast. Usually they have hemolysis (rupturing of the red blood cells) which makes them anemic and their urine dark, and eventually they get yellow mucus membranes - gums, whites of the eyes, etc.

Sometimes dogs with spleen tumors will have internal bleeding episodes and look like this.

I wish that I could give you some helpful information or suggestions, but long-distance diagnosis is just a little too tricky in a situation like this.

Best wishes.


Four years ago my adopted heeler mix was heartworm positive and my vet wanted me to give him the fast kill method. I was told it would cost around $2000 for the total treatment, and short of taking out a loan, this was not an option for me financially. I went to a second vet who told me about the Heartgard method. I decided since he was in stage one, very healthy, young, and only had a "weak positive" for heartworms to go with giving him heartgard.

I didn't restrict his activity because my vet didn't mention it would be risky and he came through it just fine. A year later he was heartworm negative and he is a very happy, healthy and active 5 year old dog now! I just took him to my vet who was very interested in the treatment I chose and did some extra blood work on him. All his tests came back great and the vet said he is a very healthy dog. I think evidence will continue to mount for using Heartgard to treat mild cases, especially if you are worried about the cost of treatment.


Hello, Rocco,

I am glad that you had such a good experience. My own results have not been nearly so good with the "soft kill" method. Dogs have remained positive three years out in some cases.

The American Heartworm Society officially withdrew its approval/recommendation of the procedure this year.

I am glad that it worked well for you, but overall we are really losing confidence in getting good results.

I cannot imagine a place where they charge $2,000 for heartworm treatment. That's about four times what we charge. You must be in Beverly Hills or someplace where practice overhead expenses are through the roof.


My 18 month rescue lab tested negative for heartworm in Feb 2011. We got him in March and unfortunately did not continue to give him the heartworm preventative (we live in NY and honestly were never expressly encouraged/educated about giving it).
So, six months later we brought him to the vet and were horrified to hear that he tested positive.
The vet is treating him with Worm Shield (ivermectin / pyrantel) once a month, Doxycycline (300mg/day)for a few weeks and Prednazone 30 mg 2x a day, which will be tapered down.
Injections were discussed but she wants to start treating him first with this method and may give injections in the future.
I am freaking out about this! The only consolation is that he probably got bitten before we got him and had the "false negative" test because there was no antigen present 6 months ago. Am I right? He came from South Carolina.
Luckily, he is showing no symptoms. Unfortunately he is an active dog...we, of course, have limited this!
Can you please give your thoughts on this treatment??


Hello, Donna,

Your veterinarian is doing exactly what I would be doing, and following the best recommendations of the American Heartworm Society.

We hope that Immiticide (the drug that actually kills the heartworms) will become available again soon, but right now you cannot get it.

Even if your doctor had a ton of the Immiticide, many veterinarians (myself included) pre-treat for one month with doxycycline to make the worms smaller and weaker.

You can search the blog for the post on doxcycline.

It sounds to me like you are in good hands.

Good luck, and thanks for reading and writing.

Tracy Powers

On March 22, my St. Bernard (4 yrs) and my Boston Terrior (8 yrs old) tested positive for heartworm. It is all my fault since they are mostly house dogs I didn't think I needed to worry about mosquitoes. I was horribly wrong. We live in Tennessee. My vet only mentioned one treatment - the fast kill. St. Bernard's Immiticide treatment will cost $780 and my Boston will cost $440. After researching all day I've read up on the slow-kill method which is more in my price range.

If I decide on the Heartguard/doxy/prednizone method will the adult worms continue to live? Will this only kill the young ones? What happens to the adult ones? How do any of them finally get out of their body? Stool? Cough up? If they do cough them up in a crate - couldn't they eat them?

My St. Bernard, who has always been gentle, very uncharacteristically attacked my brother a couple of weeks ago and drew blood. I could have killed him that day. Yesterday was the first time I had to tell a child that she couldn't pet him and it about broke my heart. I just don't trust him now. Which also adds to my confusion as to what to do regarding treatment.

Both dogs like to lay around, the St. moreso than the Boston, but I can keep both in small areas.

I just want someone to tell me what to do! Or help me decide. I've read all the questions and your answers on this site about this. If Immiticide wasn't available, what would I do exactly for the slow kill and what can I expect 1 -2 -3 years from now.


Hello, Tracy,
The so-called "Slow kill" or "soft kill" method is really a not much of any kill at all method. It is unreliable. It should keep you from getting any more worms than you already have. It iwll be years before the worms die of old age, or maybe a little sooner with the medicine.

This had a bigger following before we ran into the problems with apparent lack of efficacy in even preventing heartworms, much less curing them.

When the worms die, they shift position, being carried downstream in the pulmonary arteries until they reach one too small to pass through. They lodge there, blocking it partially or completely. This blockage of the artery is where the risk factor comes in. You've heard you shouldn't get an air bubble injected -- a 12 inch worm is worse.

The worms do not pass out of the body. Instead, the white blood cells (too tiny to be seen without a microscope) have to eat them. This takes four to six weeks to get the blockage dissolved and the arteries opend.

When you treat with Immiticide, you know when this mess will be happening. With long-term Heartgard use, you have no idea when this will occur.

Ideally you would keep the dog's activity restricted during the period when the worms are being dissolved. Can you do this for years? Not really.

Signs that you may see with the worms blocking the arteries include coughing, difficult breathing, loss of appetite, fever, coughing up blood, or just generally feeling bad.

The treatment is nto the greatest. No matter how few worms and how careful we are, there is always the chance of some complications. However, most dogs do well when treated in monthly stages -- pre-treatment with doxycycline, then a half treatment with Immiticide, then the full treatment with two days of Immiticide. In our practice we start the dogs on prednisone at the time of the Immiticide injections. This helps minimize the inflammatory reactions in the pulmonary arteries when the worms move.

I wish this were simple and easy, but it's not.


I've read so much I am sick.
Rescued my shih tzu mix 7 months ago, he tested negative by agency's vet. My vet did not retest (though he did health exam) untiil 6 mnths later, and he is positive. Vet gave me 2 options, suggesting we start with Heartguard. He has been on Trifexis since i have him.
I read that the fast kill drug may or may not be available? And that dog has to be crated for up to 9 months. I work and worry i wont be able to take care of him. And then he may die passing the worm anyhow.i cannot afford to leave him at vet for extended time.
Should i just put him to sleep?
How do you keep a dog from exercising? Is my dog infectious to other dogs, does he need to be kept inside all the time, i live in s.c. what kind of life is that for a young dog?
How do I know what to do?


Hello, Pat,

Be calm. All is not lost.
If the dog tested negative 7 months ago, then you are looking at one summer's mosquito exposure, which probably does NOT equal very many worms.

If there are microfilaria (microscopic baby heartworms) present in the blood, then Heartgard is considered safer than the Trifexis (the active ingredient sometimes causes a reaction with the babies in the bloodstream).

Immiticide (the fast kill drug)is available. There was an older approach of just keeping them on Heargard, sometimes called "slow kill" or "soft kill". Now called "probably no kill", and not recommended. You just don't know if the worms will die any time in the next few years, and you're not going to be watching the dog closely and restricting its exercise for a few years.

After a dog is treated with Immiticide to kill the heartworms, we try to limit their exercise until the body has had time for the white blood cells to dissolve away the heartworm. This takes about 5 weeks. We don't want the dog to have a rapid heart rate and higher blood pressure (from vigorous exercise), as that could shove the dead worms tighter into the artery, and maybe cause a blow-out of the blood vessel.

Most veterinarians are treating dogs in two stages now: a half-treatment of a single Immiticide injection, followed by the full 2-day treatment one month later.

Thus, you would need to restrict the exercise for about 9 weeks, not nine months.

Walking on a leash is fine. Being in the house if fine. Supervised in a fenced yard is okay. No running loose, and you don't encourage him to chase stuff. You do your best to make him a couch potato during this time. He doesn't have to be in a cage.

It is true that he could have bad complications when the worms die after the treatment, but the odds are in his favor, since he likely has very few worms. It is also true that if you don't treat him, there is a remote chance that a worm could damage an artery and cause bleeding into the lungs.

If the dog is not very active, you could elect to just keep him on the Heartgard so that he doesn't get any more worms than he has. He might do okay with that, but I generally prefer to get them treated and cleared out.

The only way that the parasite is transmitted is via mosquito bites. Your dog may be a source of infection, but he's one of hundreds, so don't feel any guilt on that. If you locked him away, there would still be lots of sources of infection. You wouldn't be saving any other dogs.

It is very unlikely that you would need to leave him at your veterinarian for an extended time.

No, you shouldn't just put him to sleep. I'm guessing that everything seemed fine until you got the blood test. So everything is not that bad.

Your veterinarian who is actually seeing your dog is your best source of advice. Do not be ashamed to ask more questions until you feel like you have a good understanding of this complicated disease. If you don't let your doctor know you have questions, he/she thinks everything is hunky-dory.


Just adopted a hound mix from a shelter and she is heartworm +. She also is currently being treated for a Upper Respiratory Infection. My vet wants to wait until we cure the infection before even giving her heartguard. She is between 2 and 3 years (estimated by vet) and from a shelter in Central Florida. What are the chances that she has a large amount of heartworms. I am not wild about the fast kill treatment for her since she has already been through so much. How long can we wait before we start either treatment? Will an xray be sufficient for determining how severe the infection is? So many question...and the more I read on line the more questions I have. I would appreciate and answers you can provide. thanks.


Hello, Susan,
If your veterinarian is in Florida, then I am sure that he/she has experience in evaluating and treating heartworm cases. If you live in a mountainous area (i.e. no mosquitos), then maybe not so much.

Generally speaking, the doctor seeing your dog is the person best equipped to advise you.

I would not personally have any problems with starting Heartgard at this time. I would not want the dog to acquire more heartworms than it already has, which it certainly will do if no preventive medicine is given this summer.

I would not have any confidence that the Heartgard will improve the situation with the heartworms that are already present.

An X-ray will determine how much damage is occurring in the pulmonary arteries, and whether the heart has been suffering long enough to become damaged, as well.

This is important information. Obvious damage on an X-ray means that you have a substantial number of adult worms present. The more worms you have, the more likely it is that the dog will have rapid progression of the disease, and also the more likely you are to have some complications from treatment. It is the downstream flow of heartworms, and subsequent arterial blockage that causes our problems. More heartworms equals more blockages.

Blood tests for heartworm are pretty much yes or no. They aren't very helpful in quantifying the number of worms, say 8 versus 80.

A dog with a good chest X-ray may still have quite a few heartworms, but has a better prognosis than a dog with obvious damage present already.

Chances of her having a large number of heartworms depend on how much she was outside, and for how many mosquito seasons, and how bad the mosquitos are in the area. Tons of mosquito exposure equals more heartworms.

At this point, I would say that when you get your recheck on the respiratory infection, you would want a chest X-ray and talk with your veterinarian about your next step.

In this situation, I would generally be starting Heartgard, and a month's course of doxycycline (though doxycycline is in short supply right now, so we are being pretty stingy with it). Then I'd start with the first single injection of Immiticide. I've written a lot about this, if you search the blog for heartworm articles.


Our rescue dog who we just adopted 3 weeks ago tested + for h.w. She's so sweet and loves us so much already and the feelings are returned. We're onboard to see her thru the recommended Immiticide protocol (after 30 days of doxycycline) and will do what we need to do to keep her quiet. The only thing we're having a hard time understanding is how to keep her quiet when we come home. She gets so excited when she sees us - wags her whole body and jumps. This only lasts about a minute or so. Will it be dangerous for her once she gets her first Immiticide injection? We've learned enough to know we shouldn't take her for long, brisk walks, or play catch with her, but will this burst of excitement when we get home be problematic? It happens a few times a day because I mostly work at home and go in and out for meetings. I don't know how to stop her from getting so excited.
Thanks so much for any advice


Hello, JJ,

It is neither possible nor desirable to have the dog lie still for weeks at a time.

We try to avoid situations that result in prolonged increased heart rate and blood pressure (such as strenuous exercise).

Yes, the heart rate and pressure do rise when the dog gets excited, but this is unlikely to be a problem.

Yes, try to minimize it, but these short periods of excitement are not likely to cause major difficulties.

It would not be better to keep her sedated for weeks at a time. Crating her 24 hours a day would make her quality of life not so great, and would not make that much difference in how she responds to treatment.

That sort of thing is best reserved for a dog who is actually having problems.

So, do the best you can to keep her chilled out, and don't beat yourself up because she's glad to see you.

If something doesn't seem right, let your veterinarian know as soon as possible. Look for coughing, fever, loss of appetite, difficult breathing, or just generally feeling bad. If you see any of these things, let your veterinarian know.

Tim and Linda

My dog is 14 years old. We took to Vet for arthritis and he was put on Carprofen. 3 months later he has developed a gagging that is persistent. There is no vomiting. He is also on Cindamycin 150mg for RED gums. My vet wants to put him under and give him extensive teeth cleaning and possible extraction of 1 or more teeth. He is having labored breathing but still has a good appetite. He has to have soft food because of the gums. Another vet says at his age just think of all the good times we have had together. I don't know if he is in a lot of pain and don't know what to do. Does this sound like heartworm? He is an abandoned puppy with his eyes still closed. He is so loyal. I cry daily wondering what is best for him. Please give me your opinion. I hate to say it, but we are on a tight fixed income. The 2nd Vet also said it would cost a lot of $ to run the xrays, EKG, Cat Scan, blood work, etc. Thank you in advance for any info you can give me.


Hello, Tim and Linda,
This doesn't sound particularly like typical heartworm disease.

At fourteen years old, a lot of things could be going wrong with the wear and tear of age.

Having a bad mouth with gum disease and loose or damaged teeth can certainly make a dog feel bad, and have a poor quality of life.

It would be beneficial to get that handled, but there is increased risk with anesthesia in an older patient, particularly one that seems to be sick.

X-rays, blood-work, and ECG let you find out what else may be wrong with the dog, and they also help you to manage the anesthesia so that it is as safe as possible.

If you just had the teeth fixed, this would require anesthesia, and you might run into some complications that could have been avoided if the tests were done ahead of time.

If the alternative is putting the dog to sleep, then I'd take the risk and try to get the mouth handled. You might lose your friend in the process, but if the alternative is putting him to sleep right now...

Of course, the teeth might not be the biggest problem. That is why your doctors have recommended the tests.

I wish that I could sort this out for you, but I haven't even seen your dog. Your best source of information is the doctors who have seen him.

I wish we could just look at the dog and "know what's wrong", but often we cannot see what we need to see from the outside. That is why the tests are recommended.

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