The parasitic worm responsible for heartworm disease is called Dirofilaria immitis.

The life cycle of this parasite begins when an infected mosquito lands on your pet to feed. 

The larvae enter the pet’s body through the mosquitoes bite and migrate through the cat or dogs tissues. The larvae develop over the next few months eventually reaching the pet’s heart and lungs. 

Heartworms may be present in the heart and lungs approximately four months after initial infection. Once in the pet’s heart, the worms can grow up to 7 to 11 inches in length and cause significant damage to the heart and lungs. If left untreated, heartworm disease may result in death.