Heartworm disease is described in a 14-month-old neutered female ferret (Mustela putorius furo) which had a three week history of sneezing, anorexia and dyspnoea. Echocardiography revealed the presence of heartworms as hyperechoic densities within the right atrial and ventricular cavities. At necropsy, four Dirofilaria immltls parasites (three females, one male) were found in the right heart, the cranial vena cava and the caudal vena cava. Histopathological findings were similar to those reported in canine heartworm disease. Echocardiography may be a useful method of diagnosis of heartworm disease in the ferret.