Heartworm disease is caused by a parasite named Dirofilaria immitis. It is transmitted through the bite of an infected mosquito. When a mosquito bites an animal, it sucks blood. If the animal is suffering from heartworm disease, the parasite will be sucked by mosquito and it multiplies in the body of mosquito. When a healthy dog or cat is bitten by such infected mosquito, he can get heartworm disease. Heartworm infection is a serious problem in cats and some cats may die without showing characteristic symptoms. The symptoms shown may not seem related to the disease. Cats suffering from heartworm disease sometimes develop cough and look tired all the time. Some show vomiting as well. Death can occur suddenly. Diagnosis of heartworms can be a difficult task because the number of worms is small. But the problem is that even a small number of worms are able to cause inflammation. Radiographic technique such as heart ultrasound and blood tests can be helpful in the diagnosis of problem. So far, there is no treatment against heartworms. Symptomatic treatment is given to reduce the inflammation caused by the worms. Sometimes surgical intervention is necessary if the cat is severely infected. Prevention is vital against heartworms. Prophylactic treatment is given against heartworms. Injectable and tablets should be given regularly as they save pets from heartworms.