Dog Heartworm Test

Heartworm disease is present throughout North America and is not just a disease that affects dogs who spend a great deal of time outdoors. Heartworm can affect any dog of any age and size from a Chihuahua to a Great Dane – it only takes one infected mosquito to transmit the disease!! Prevention is the best way to protect your dog from heartworm – help your dog remain heartworm free. Ask us how we can work together to keep this disease under control and reduce the risk for your canine companion.

What are the symptoms of heartworm disease?

For dogs affected by heartworm, there are initially no clinical signs seen, and they can act completely normal. As the heartworm progresses, respiratory symptoms (coughing, having trouble breathing, tiring more quickly after exercise) are the most common to see. Nosebleeds can occur, and if the disease progresses, the affected dog can develop heart failure.

How do dogs get heartworm?

Heartworm is a parasite that is passed through mosquitoes when the weather is consistently over 14°C. A mosquito bites an infected dog and passes a baby (larva) heartworm to the next dog that they bite. These baby heartworms can grow into adult worms, which live in the heart and the arteries around the heart. The adult heartworms can reproduce, and continue increasing the number of worms in the affected animal.

How do we diagnose heartworm disease?

Heartworm is typically identified with a blood test, which tests for the presence of any adult heartworm in the bloodstream. Since it takes about six months for baby heartworm to develop into adult heartworm, we do this blood test six months after the last possible exposure to heartworm in the season. In London, our last possible heartworm exposure is typically in October, so we test the following spring (April or May), as this is six months after the last exposure from the year before.

What are the treatment options for heartworm disease?

Prevention options are available from all veterinary clinics. These are given once a month for the heartworm season, and work to kill off any baby heartworm before they develop into adult heartworm. They are available in tablets or chews taken by mouth, or liquids applied to the skin at the base of the neck. For London, our prevention is given from June-November. Each treatment works to kill off any heartworm exposure from the month before (so we are protecting from May-October) as this is the season that can have weather over 14°C consistently. If our clients are travelling to Florida or other southern locations in the winter, heartworm prevention is recommended year round, as the warmer weather permits heartworm to be passed all year. If heartworm progresses from the baby heartworm stage into an adult heartworm infection, this can be treated. It involves a 12-month protocol of medications and strict rest to clear the adult heartworm from the body. Unfortunately, even with treatment, it will not be able to undo any damage created to the heart and lungs from the adult heartworm – which is why prevention options are preferred.


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Last updated: March 16, 2022.

Dear Clients,

We are happy to announce that we will be allowing clients inside our exam rooms again! 1 person per pet will be allowed into the building. Masks must be worn for the duration of the appointment, even after March 21, 2022.


This includes vaccines, wellness exams, blood work, heartworm testing, spays and neuters, dental services, and more!



If you wish to connect with a veterinarian via message, phone or video, visit our website and follow the "Online Consultation" link. You will be connected to an on-call veterinarian that may be located at a different hospital.


Have you welcomed a new furry family member to your home? We’d love to meet them! Visit our Must Know New Pet Owner Information page for useful resources and helpful recommendations for new pet owners.


We are OPEN with the following hours:

Monday - Thursday: 8:00 am - 7:00 pm
Friday: 8:00 am - 6:00 pm
Saturday: 8:00 am - 1:00 pm
Sunday: CLOSED


Thank you for your patience and understanding and we look forward to seeing you and your furry family members again!

- Your dedicated team at Fairmont Animal Hospital