Heartworm disease in dogs and other animals is caused by the parasite Dirofilaria immitis. Transmission occurs through the bite of an infected mosquito, which carries the larval stage of the parasite, known as microfilariae. These larvae enter the bloodstream and, over approximately six months, mature into adult worms that can inhabit the heart, lungs, and arteries. This parasitic infestation can severely interfere with the animal’s vital organ functions and, if left untreated, may result in death. Regular preventive treatments and veterinary check-ups are crucial for managing this risk.