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Heartworm: Introduction

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All Dogs are at Risk

All dogs are at risk for potentially deadly heartworm disease. Heartworms live in the heart and blood vessels of the lungs of dogs, cats and other mammals like wolves, foxes and coyotes. Heartworms cannot be spread directly from animal to animal without a mosquito as an intermediary.

Heartworm: Introduction


Heartworms are spread when a mosquito bites an infected dog and picks up tiny larvae called microfilariae from the bloodstream. Then that mosquito bites another dog infecting it with the heartworm larvae.

Over the next several months the heartworm larvae grow and migrate to the heart and lungs. These larvae mature into adults, which can be a foot in length, and they produce microfilariae that circulate in the bloodstream. Now this dog is a reservoir of heartworms and is ready for another mosquito to bite and infect yet another dog.

Untreated, heartworm disease can lead to severe problems with the heart, lungs, liver and kidneys and may result in death.

Important Safety Information:
HEARTGARD (ivermectin) is well tolerated. All dogs should be tested for heartworm infection before starting a preventive program. Following the use of HEARTGARD, digestive and neurological side effects have rarely been reported. For more information, please visit

Click here to download full prescribing information.

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