Second degree AV block in a dog with cardiac hemangiosarcoma in the interventricular septum

A 13-year-old, male, neutered Maltese presented for lethargy and anorexia. Clinical examination identified bradycardia and a grade 2/6 systolic left basilar murmur. A six-lead electrocardiogram revealed high-degree, 4:1 second-degree atrioventricular block, with a rate of 40 beats per minute. Echocardiography revealed a large mass in the interventricular septum, an atypical location for a cardiac mass, as a potential cause of the arrhythmia. An epicardial pacemaker was placed and a mass within pericardium was biopsied. Histopathology revealed hemangiosarcoma. The patient was treated with chemotherapy and radiation therapy and was euthanased 2 months following diagnosis.