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Heartworm Symptoms That All Dog Owners Should Recognize

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Dr. Mark is a veterinarian. He works mostly with dogs and exotic animals.

Recognize the symptoms of heartworm disease and protect your dog.

Recognize the symptoms of heartworm disease and protect your dog.

When dogs are first bitten by mosquitoes infected with heartworm microfilaria (Dirofilaria immitis), they show no symptoms. That stage lasts for six months! By the time your dog is showing symptoms, things have been going on for a long time, so recognize these symptoms as soon as they start.

What Are the Symptoms in the Different Stages (Classes) of Heartworm Disease?

  • Class 1: Your dog may not even have symptoms at this stage. He might have mild symptoms like an occasional cough.
  • Class 2: Things are getting a little worse. His symptoms are usually still mild, like an occasional cough, and he might be more tired than you would expect after very light exercise, like just running around the yard chasing a ball.
  • Class 3: At this point, your dog will start losing weight, be tired most of the time, and will cough more often. He will probably faint occasionally and show signs of congestive heart failure, like ascites (fluid on the abdomen).
  • Class 4: The heartworms are causing a blockage at this stage, so the symptoms are severe. He will experience constant coughing, exhaustion, and weight loss because he will find it uncomfortable to eat. When your dog is at this stage, known as caval syndrome, it might be too late to save him. You have no excuse to let a dog reach Class 4.
If your dog has any symptoms of heartworm, she should be taken to the vet for testing.

If your dog has any symptoms of heartworm, she should be taken to the vet for testing.

Her lungs and heart will be examined during her exam.

Her lungs and heart will be examined during her exam.

Alternatives for a Heartworm Positive Dog

The first thing you need to do is take your dog to your veterinarian and have his blood tested. If the antigen test is positive, that indicates he has been infected with heartworms. He probably has at least 15, but maybe as many as several hundred adult worms in the heart.

If your dog tests positive, do not start worrying. There are alternatives.

  1. The first alternative, and the one suggested by most veterinarians, will be to give your dog injections of immiticide, an arsenic injection that goes into the muscles of the dog's back and causes the adult heartworms to die off. It is the quickest way to get rid of the problem, and the worms cause less damage to the heart, but it is also expensive and can be dangerous. If you take your dog home and he or she runs around after the injection, the activity can cause the dead worms to be broken off in a mass. The mass can cause a blockage in the dog´s lungs and they might die.
  2. The other alternative is to put your dog on a safe heartworm therapy. She is given ivermectin every month for several years. This does not cause the adults to die—they go on infecting your dog´s heart. It does keep them from reproducing, however, and when all the adults die, your dog will be heartworm free. This treatment is not recommended by most veterinarians since the adult worms are not killed. They will go on infecting your dog, and if she already has clinical heart disease, most vets want those worms out of there as soon as possible.
  3. The last alternative is to use safe herbal heartworm therapy. There is controversy around whether this therapy is effective, but if you are against giving yourself and your dog chemicals (like ivermectin), it is an alternative. Like safe heartworm therapy, this will not kill the adults.

How Long Will My Dog Live With Heartworm?

Your dog's life expectancy after being diagnosed with heartworm is not really known. Some dogs will have a small burden and live for years. Smaller dogs can develop congestive heart failure with only a few worms in the heart and will die within a few months.

You will have to decide which of the alternative treatments to use based on the size of your dog and the degree of damage already done to your dog´s heart. Discuss this issue with your veterinarian, but ultimately it is up to you to decide.

If her heartworm test is positive, you have several options.

If her heartworm test is positive, you have several options.

How to Prevent Your Dog From Becoming Infected

You should have your dog on a heartworm preventative. Unfortunately, some dog owners do not prevent heartworm disease because the manufacturers of heartworm preventative charge a big markup, and then the veterinarians that distribute this product charge another markup.

If you cannot afford the prices your vet charges, the alternative is to buy a large supply of ivermectin, the heartworm prevention available in Heartgard. You still need to dose your dog monthly, and the product is so cheap that I recommend you do so throughout the year. The chance of your dog getting infected in the winter is minimal, but so is the cost of the drug, and in my opinion, it is not worth the risk.

You can buy a sheep formula online or purchase it from your local feed store. The doses are available in my other article on cheap heartworm prevention. If you have a Collie or other herding dog breed, your dog may be sensitive to ivermectin and this may not be right for you. You can read more details about testing in the other article.

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If you do not want to give your dog monthly ivermectin, there are also some holistic vets that recommend an oral herbal or homeopathic heartworm preventative. I do not recommend this and believe you are taking unnecessary risks with your dog's health. If you want the various formulas, you can speak to your holistic vet or look at another site.

Stray dogs are likely to become infected at an early age because they are outside all the time, but even inside dogs can become infected.

Stray dogs are likely to become infected at an early age because they are outside all the time, but even inside dogs can become infected.

Will Your Dog Become Infected With Heartworm?

If you keep your dog on heartworm preventative every month, you do not need to pay for yearly testing. Some states and regions (like Georgia and the Mississippi valley), however, have reported an increase in heartworms resistant to the traditional preventatives, like ivermectin. If you live in Georgia, Alabama, or the lower Mississippi valley area, please read up on preventing resistant heartworm.

This is a preventable disease. Do something about it today.


Noack, S., Harrington, J., Carithers, D. S., Kaminsky, R., & Selzer, P. M. (2021). Heartworm disease - Overview, intervention, and industry perspective. International journal for parasitology. Drugs and drug resistance, 16, 65–89.

Bowman, D. D., & Drake, J. (2017). Examination of the "susceptibility gap" in the treatment of canine heartworm infection. Parasites & vectors, 10(Suppl 2), 513.

Maxwell E, Ryan K, Reynolds C, Pariaut R. Outcome of a heartworm treatment protocol in dogs presenting to Louisiana State University from 2008 to 2011: 50 cases. Vet Parasitol. 2014 Nov 15;206(1-2):71-7. .

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

Questions & Answers

Question: How can I treat my dog at home against heartworms?

Answer: You can order generic Heartgard (ivermectin) from many sources on the internet, without a prescription. You can also give sheep drench orally to prevent heartworm infection.

© 2013 Dr Mark


CAguilar1 on April 19, 2019:

Thank you so so much Dr. Mark! I appreciate all of your help and responding to my concerns. I have not checked out the Ivermectin but I will certainly do that. I have scheduled a follow up appointment with my vet as well. Thank you again for responding and sharing your wisdom, it is much appreciated!

Dr Mark (author) from The Atlantic Rain Forest, Brazil on April 17, 2019:

I am not sure that the black walnut works but compared to the alternative, the strychnine injections, it looks worth trying.

Have you looked into the slow kill method with ivermectin? You do not kill the adults, only the young, and as the adults get old they die anyway so your dog does not develop clinical heartworm disease. As long as your dogs are not clinically positive it is a great alternative.

As far as your questions, I would definitely stop the prednisone. It is not going to help. There is no problem with the Interceptor dose you gave. If they were my dogs I would continue with the doxycycline to treat a secondary bacterial infection, but this may or may not be necessary. (No one can tell you for sure.)

I think you should avoid the ambertech products. Hawthorn berries are not going to destroy the heartworms that will evenually kill your dogs.

CAguilar1 on April 17, 2019:

Hello Dr. Mark, I have 2 large breed dogs that recently tested positive for heartworm within the last week. My vet started them both on the typical protocol of Doxycyclyne and Prednisolone and wants to do the standard procedure with harsh injections.

After doing research on all possible treatments I don’t want to go through with the standard procedure. I have decided I want to use a natural alternative. My main concern is this, they have been on the steroid and antibiotic for a little over a week. Also there was miscommunication between my vet and myself, he also gave me a box of Interceptor Plus which I inadvertently gave to both of them along with the steroid and antibiotic. I realized later I was not supposed to administer the interceptor until much later.

My concern is knowing I gave them the interceptor is it safe to still start with the natural approach?

Also do I stop the antibiotic and steroid before starting the natural treatment or keep doing that along with the natural treatment?

I am considering either using the Amber Technology HWF product or the protocol prescribed on website which entails the following:

-Black Walnut - Artemisia Combination - HSII - COQ10

LongTimeMother from Australia on September 20, 2015:

Thanks for your response, Mark. Local vet says it is poisoning, probably from eating a baited mouse, with no mention of heartworm. I've written more to you in the forum. Thanks for being such a helpful vet.

Dr Mark (author) from The Atlantic Rain Forest, Brazil on September 20, 2015:

LTM, dont you live in an arid part of Australia? You may not even have endemic HW there. Before you go in, try to catch some sputum in a plastic bag (in case the dog will not cough during the exam!). It may be some sort of lungworm, not sure what is a problem in your area.

If the dog is old it may be a tumor. Hope everything goes all right.

LongTimeMother from Australia on September 20, 2015:

Hi Mark, I have been minding one of my adult kid's dogs while she's working overseas ... and it is coughing (or more like loud panting) up blood. Waiting for the local vet to open. Does this sound like heartworm?

B A Tobin from Connnecticut on April 09, 2013:

Thank you for clarifying that! Yes, I hope it does help her help her dogs..but I can't impose my opinion, so informational material is just the right way to go about it. :) I will lead her to your site, but I can't make her drink.

Dr Mark (author) from The Atlantic Rain Forest, Brazil on April 09, 2013:

Sorry I misunderstood your post and thought you were asking about the once a month preventative. It does not have any arsenic in it, just the treatment, which is given deep in the back and is very painful. (The safe therapy is much better, in my opinion).Some people do not like to give their dog the prevention every month, as it is a chemical, but I think it is the worse of two evils! Thanks for sharing this with your acquaintance, I hope it helps.

B A Tobin from Connnecticut on April 09, 2013:

It was mainly to confirm my previous understanding of prevention..did I read correctly that arsenic is in the medicine?? That would be unusual in my mind ...poison to give once a month, but if I did read correctly, it would be the lesser of two evils in a minute dose.

What are the properties in immiticide or the treatment? Do I have that right?

Wow thank you for your information and response to my inquiries!

Your article makes a reader SEE the disgusting and horrible possibilities! I voted thumbs up and useful for this and will refer to an acquaintance who does not believe in medicine for her dogs...recall I stated "acquaintance" Perhaps if she saw this she may change her mind.

Dr Mark (author) from The Atlantic Rain Forest, Brazil on April 09, 2013:

Yes, in almost all parts of the US monthly heartworm preventative is recommended. Some areas (like northern Montana) may be okay, but the prevention is so safe, and so cheap, that it is really a good idea about everywhere. Since you have several dogs (I don't know how much your JRTs weigh) the sheep product is probably the best for you.

Be sure to read that article when you get a chance and leave me a note if you have any questions about it. Was your question about the heartworm prevention or another product? The other worms are really not much of a concern in an adult dog, but the heartworms are something that should be prevented.

B A Tobin from Connnecticut on April 09, 2013:

Wow Dr Mark1961, this article is a real eye-opener. You don't realize the impact of not giving your dog the once a month wormer the vet recommends even without any sign of worms until you see the pictures of a dog's heart with the worms! Ugh! and the symptoms, so sad. Thank you for your thorough article.

By the way, is that traditional of a Vet to tell you to give a monthly wormer even for my dogs without heartworm?

Dr Mark (author) from The Atlantic Rain Forest, Brazil on February 26, 2013:

Thank you, Thelma, I appreciate your visit.

Thelma Raker Coffone from Blue Ridge Mountains, USA on February 25, 2013:

Thanks for another informative article. I enjoy reading your hubs very much!

WillStarr from Phoenix, Arizona on February 24, 2013:

She's nine months.

Dr Mark (author) from The Atlantic Rain Forest, Brazil on February 24, 2013:

The dose for a 3 pound dog is really, really small, so if you can afford the commercial product it is a better idea.

How old is she now? 3 pounds. Wow. That makes my Maltese look like a Giant Dog Breed.

WillStarr from Phoenix, Arizona on February 24, 2013:

My only concern is that our chihuahua is so tiny. She weighs just three pounds, so I guess we'll stick to the commercial dosage.

Dr Mark (author) from The Atlantic Rain Forest, Brazil on February 24, 2013:

If you have any financial worries and the Heartgard is too expensive, be sure to click on the hyperlink to the sheep formula. It is ivermectin, the same drug, but you can buy a 3 year supply for about what 6 months of Heartgard costs. The dosing rate is in the other article.

I live on the beach (lots of mosquitoes) and have to give heartworm prevention year round so it is worth it to me, but since my dog is big I just bought a bottle of the cattle formula at my local feed store.

Thanks for reading and commenting!

Elizabeth Hanks from Queen Creek on February 24, 2013:

Another great article! Both of my pups are getting on Heartgard sometime next month. Things have been hard for my fiancé and I financially for a while, but like I've been telling him for months, that's no reason to neglect our dogs' health!

Prevention is definitely the best way to go with just about any infectious disease in the pet world, whether by monthly meds, vaccinations or even feeding them higher quality food!

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