What is Heartworm?
Heartworm is a serious disease caused by worms (Dirofilaria immitis) that live in the heart, lungs and blood vessels of infected dogs. It's spread by mosquitoes — just one bite from an infected mosquito can transmit hundreds of heartworm larvae.
Left untreated, heartworm disease can cause lung disease, heart failure and damage to other organs.
What Heartworm Looks Like
These are adult heartworms removed from a dog's heart and blood vessels.
Yes, they are as bad as they look.
This is why prevention is so important.
This is why prevention is so important.
Signs of Heartworm in Dogs
Early signs can be mild or easy to miss.
✓ Mild cough
✓ Reluctance to play
✓ Tiring more easily
✓ Breathing harder
✓ Less exercise tolerance
✓ Weight loss (in advanced cases)
This page is for educational purposes only and does not replace veterinary advice. Always follow your veterinarian’s guidance for testing, prevention and treatment decisions.