Heartworm or also called dog heartworm is a parasitic roundworm that is spread from host to host through the bites of mosquitoes The definitive host is the dog, but it can also infect cats, wolves, and other animals, such as ferrets and sea lions, and even, under very rare circumstances, humans. Parasite is commonly called "heartworm" however, adults often reside in the pulmonary arterial system as well as the heart, and a major effect on the health of the animal is a manifestation of damage to the lung vessels and tissues. Occasionally, adult heartworms migrate to the right heart and even the great veins in heavy infections.