Heartworm Disease Testing, Treatment & Prevention

What is Heartworm Disease?

Heartworms are 8″ long spaghetti-like worms that live inside a dog’s heart and can cause potentially life-threatening heart disease. These adult worms produce hundreds of microscopic larvae that circulate in the blood of the infected host (dog, coyote, fox, wolf).

Heartworm disease is transmitted when a mosquito bites and ingests blood from an infected host and then later bites an unprotected dog thus passing the larvae along.  Over the ensuing 6 months the larvae travel to the heart and develop into mature worms.

Unfortunately we cannot rely on the absence of clinical signs to consider your dog free of heartworm, and the earlier they are detected, the better the chances are for recovery.


Six months or more after transmission via a mosquito bite, heartworm disease can be diagnosed using a simple blood test. If your dog has been through a summer season without the benefit of heartworm preventive medication, a heartworm blood test should be performed before initiating preventive measures.

If your dog has symptoms of heart disease (coughing, laboured breathing) a heartworm blood test may also be indicated. Intermittent heartworm testing is also recommended for all dogs on preventive medication (once every 2 years) in order to confirm compliance.

Please speak with our staff if you are unsure whether your dog is due for a heartworm test.

Heartworm Prevention for Dogs in Oakville

Although the incidence of heartworm disease in dogs living in the Oakville, Ontario area is low, because of the severe nature of the disease, we do recommend preventive measures for your dog. At this time there is no effective vaccine that can protect dogs against heartworm disease, as there are for diseases such as rabies and distemper.

However, there are several safe products available that effectively prevent heartworm disease. They come in a variety of formulations all of which are administered once monthly for 6 months during the mosquito season (first dose June 1st, last dose Nov 1st).

There are several differences between the products used to prevent heartworm disease. Some are given orally, and others are applied topically. Some will provide additional protection against other parasites such as fleas, ticks, mites and intestinal parasites.

Our veterinarians will help you decide which preventive medication best suits your dog’s lifestyle.

Heartworm Products:

Revolution:  Revolution4dogs.com

Advantage Multi: Animalhealth.bayer.ca

Heartgard:  Heartgard.com

Sentinel:  Elanco.ca

Nexgard Spectra  Nexgard Spectra

If you would like more information about heartworm disease online, please see HeartWormSociety.org