Heartworm in Dogs

Heartworm disease is a serious, often fatal condition in dogs that can result in severe lung disease, heart failure, organ damage and more. Our Collingwood vets explain why preventing heartworm disease is both easier on your pet, and on your wallet than treating the disease after your dog becomes ill.


Heartworm disease is caused by a parasitic worm called dirofilaria immitis which is primarily spread through the bite of an infected mosquito.

Once infected, your dog becomes a 'definitive host' for this parasite, meaning that the worms mature into adults, mate and produce offspring. This serious condition is called heartworm disease because these worms make their home in the heart, lungs and blood vessels of infected pets.

Signs of Heartworm in Dogs

Unfortunately there are no early signs of heartworm disease. Symptoms of this condition only begin to appear in dogs once the disease has progressed to more advanced stages. When symptoms do become evident they include fatigue, swollen abdomen, coughing, difficulty breathing and weight loss.

Diagnosing Heartworm 

Blood tests can be done at your vet's office to detect heartworm proteins, called antigens, which are released into the animal's bloodstream. However, these antigens are not detectible until approximately 6-7 months after your pet has been infected. Your vet will also look for clinic signs of a heartworm infection such as fluid buildup in your dog's lungs, a swollen abdomen, coughing (in some cases coughing up blood), and poor overall condition. 

Treatment for Heartworm Disease in Dogs

The reason that prevention is so important when it comes to heartworm is that the treatment for this disease can be toxic and may cause serious health complications for your pet. Not only that, treatment is can be expensive because it requires multiple visits to the vet, bloodwork, x-rays, hospitalization, medications and a series of injections.

If your dog is diagnosed with heartworms, your vet may prescribe a 4-week course of doxycycline followed by 3 doses of melarsomine dihydrochloride (an arsenic-containing drug that kills adult heartworms). Melarsomine dihydrochloride is administered by an injection into the back muscles of the dog in order to kill the parasites. To help make the injection process less stressful for your dog the vet might also prescribe sedation medication to help your dog stay relaxed. 

In cases where immature parasites could be present your dog may also be treated with heartworm preventive medication for 2 months before beginning the melarsomine treatment.

Prednisone is also frequently prescribed for dogs during the melarsomine treatment to help prevent complications. Strict crate rest is essential throughout your dog's heartworm treatment.

Heartworm Prevention

Keeping your dog on preventative medication is the best way to prevent heartworm disease from impacting your dog's health. Even if your dog is already on preventive heartworm medication, it is recommended that dogs be tested for this parasite annually.

Heartworm prevention is safer, easier and much more affordable than treating the progressed disease. A number of heartworm preventive medications can also help to protect your dog against other parasites such as hookworms, whipworms and roundworms.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

Find out how to protect your dog against heartworm disease. Contact our Collingwood vets today to book an appointment for your pet.

(519) 599-7777