Heartworms parasite is that live inside the dog's heart. These types of worms are called. Dirofilaria immitis. Heartworms are transmitted via the mosquito as the carrier host. Dogs get heartworms when an infected mosquito bites them. Severe infestation can cause sudden death as heartworms can obstruct the heart and blood vessels leading to high blood pressure and causing heart failure. The symptoms of heartworms are coughing, weight loss and apathy.