When a mosquito bites an animal infected with heartworm, it becomes infected. When infected larvae bite your dog, your dog becomes infected with the larval stage of the heartworm parasite. Heartworm is a potentially fatal and serious disease in pet dogs. Spaghetti-like worms live in the lungs, heart and blood vessels of an infected pet dog, causing lung disease, organ damage and heart failure to the pet, and can be fatal if not treated in time . It is possible