Canine heartworm is a serious parasitic disease caused by the Dirofilaria immitis worm, which primarily affects dogs. The disease is transmitted through the bite of an infected mosquito, which introduces the larvae into the dog's bloodstream. Once inside, the larvae mature into adult worms, which can live in the heart and lungs, leading to severe health issues. Symptoms of canine heartworm may include coughing, fatigue, and difficulty breathing. If left untreated, the condition can result in heart failure or even death. Regular veterinary check-ups and preventive medications are essential for protecting dogs from this potentially fatal disease.