Heartworm disease is caused by the parasite Dirofilaria immitis, a type of roundworm that lives inside the heart and blood vessels of the lungs. Heartworm disease is transmitted by mosquitoes. It is a serious disease that primarily affects the heart and lungs but can also affect the liver, kidney, eye, and central nervous system, and if untreated, can cause death.
The symptoms of heartworm disease are subtle and can be easy to miss. As the number of heartworms increases, the symptoms of coughing, lethargy, exercise intolerance, lack of appetite and weight loss become more apparent. However it is best not to wait until symptoms develop since irreversible damage may have already occurred by then.