Heartworm disease is a serious and potentially fatal disease in pets in the United States and many other parts of the world. It is caused by foot-long worms (heartworms) that live in the heart, lungs and associated blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body.

The American Heartworm Society is the veterinary profession’s leading resource on heartworm information. Our guidelines for heartworm management in dogs and cats incorporate the latest science and expert recommendations.

Heartworm disease is a serious and potentially fatal disease in pets in the United States and many other parts of the world. It is caused by foot-long worms (heartworms) that live in the heart, lungs and associated blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body.

The illustration below takes you through the heartworm life cycle, step by step, and helps you understand how and when heartworm preventives work, when infection can be detected on a heartworm test, when treatment is necessary and how long heartworms live.

These guidelines are living documents and are revised periodically based on information presented at the American Heartworm Society’s Triennial Symposium, new research, and additional clinical experience.

The American Heartworm Society recommends year-round administration of heartworm preventives to ensure pets are protected from deadly heartworms. If a dog becomes infected, the resulting heartworm disease can cause life-long damage.

The American Heartworm Society recommends the following heartworm treatment protocol for dogs. This method effectively eliminates most heartworm infections when closely followed by both you and your veterinarian.

As part of our mission to lead the public in the understanding of heartworm disease, we are constantly developing informational tools and resources for pet owners. We encourage you to download, share and make use of the resources listed below.

For a detailed review of the heartworm life cycle and transmission of heartworm infection, please refer to the complete Canine Guidelines. HEARTWORM PREVENTION The AHS recommends year-round heartworm prophylaxis for maximal effectiveness. If seasonal treatment is chosen, administration should begin at least one month prior to the anticipated start

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