Primary cardiac hemangiosarcoma in a horse: echocardiographic and necropsy findings.

Cardiac hemangiosarcoma, especially primary, is infrequently reported in the horse and remains a diagnostic challenge because of vague clinical signs and difficulty to reach an antemortem diagnosis. A 17-year-old American Quarter Horse gelding was presented with a history of tongue swelling and secondary aspiration pneumonia. Initial assessment indicated dehydration, and thoracic ultrasound revealed an abnormal structure within the myocardium alongside the previously suspected aspiration pneumonia. A subsequent, complete echocardiogram identified a large, heterogeneous, ill-defined mass invading and replacing the normal myocardium of the right ventricular free wall. Because of lack of improvement the horse was euthanized, and postmortem examination confirmed primary cardiac hemangiosarcoma with no further masses identified in other organs. This case is an unusual presentation of primary cardiac hemangiosarcoma for which echocardiography played a significant role in identifying a cardiac mass.