A 58 year old man with a history of cerebral infarction was admitted to hospital with chest discomfort and dyspnoea. He had no history of precordial chest discomfort. Angiography and left ventriculography showed that coronary fistulas connected the coronary sinus with the left circumflex and right coronary arteries. His coronary sinus did not communicate with the right atrium, draining instead into a persistent left superior vena cava. Angiography showed a mass, suspected to be a thrombus, in the coronary sinus. Transoesophageal echocardiography confirmed the presence of a mass in the atrioventricular groove. The mass was removed at surgery and proved to be a cavernous haemangioma.