Heartworm

Heartworm is a parasitic roundworm that is spread from host to host through the bites of mosquitoes. The heartworm affects cats, dogs,  wolves, coyotes, foxes, and some other animals, such as ferrets and even humans. The parasitic worm is called a "heartworm" because the parasite in the final reproductive stage of its life cycle, resides in the heart of its host where it can stay for many years until it kills its host through congestive failure of the heart.