An unusual aneurysmal aorta--right atrial communication was found in a 25-year-old man with a rounded mass in the right cardiophrenic angle. Differential diagnoses included ruptured aneurysm of the sinus of Valsalva, coronary arteriovenous fistula, rupture of a dissecting aneurysm of the ascending aorta into the right atrium, and pseudoaneurysm of the right coronary artery followed by formation of a fistula between the aneurysm and the right atrium. Closure of the communication was performed under cardiopulmonary bypass. Complete absence of the right superior vena cava with a large persistent left superior vena cava draining to the coronary sinus was an unexpected finding at operation. The origin of the communication is not known; possible anomalous coronary and noncoronary origins are considered.