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What is heartworm disease?

Heartworm disease is caused when an infected mosquito transfers heartworms from one animal to the next. Foot-long worms can thrive near the heart and lungs, causing severe damage to an infected dog. It can be fatal, especially if left untreated.



A mosquito bites an infected animal and takes in young heartworms as it feeds.

In some cases, veterinarians have found several hundred worms inside a dog. Even after the heartworms have been killed, they can leave behind permanent damage to your dog’s heart, lungs and arteries.2

  • Life happens. It’s easy to forget or give monthly heartworm disease preventatives late. Year-long prevention is the best way to ensure your dog doesn’t get heartworm disease.3
  • Treatment for a diagnosed heartworm infection should be administered as early in the course of the disease as possible.2

Where there’s one mosquito, there’s risk.

Heartworm Incidence Map

Heartworm disease has been reported in all 50 states. Climate differences and changes as well as the presence of wildlife carriers cause infection rates to change dramatically every year—even within local areas. What’s more local than your neighborhood? Your own home? Most people don’t realize that infected mosquitoes can enter your house, so both outdoor and indoor pets are at risk.

Heartworm Disease Symptoms in Dogs »