It's Heartworm Season! Dr. Kerr Answers the Most Common Question

I have seen some commercials on the TV about Heartworm and that it could affect my dog. What is Heartworm and should I be concerned?


Worried Pet Parent


Dear WPP,

I too have seen the ads on TV and they do portray an important message. Heartworm is a disease that affects dogs in Ontario. The disease is passed by the common mosquito to unprotected dogs. When an infected mosquito draws blood from an unprotected dog, baby heartworms flow under the dog’s skin. These babies mature and eventually find their way to the heart which becomes their new home. These heartworms grow to a size of 10 centimeters (5 inches) and decrease blood flow in the heart causing heart failure. Each year veterinarians test dogs for heartworm and as long as they are not infected, dogs can go on a monthly preventive medication to ensure their safety during mosquito season. The added benefit is these medications usually protect against other parasites such as fleas, intestinal worms and mange (skin mites).

When dogs are tested for heartworm and the test returns positive, meaning the dog is infected, the condition is treatable, although the medications used are much more toxic than those used for prevention. It is far better for your dog to prevent heartworm disease than to treat it.  Costs for treating a dog with heartworm are the same as the costs for eleven years of prevention medication.

Having your dog tested for heartworm and then started on a monthly preventive against heartworm infection is the best way to keep your four legged family member safe, healthy and protected from this debilitating and preventable disease.

If you have any questions or concerns about heartworm, do not hesitate to get in touch with our Bolton team at North Hill Animal Hospital: or (905) 857-5057

All the best,

Dr. Kerr