Bidirectional coronary venous return in the partial unroofed coronary sinus syndrome complicated by coronary sinus orifice atresia.

Unroofed coronary sinus syndrome complicated by coronary sinus orifice atresia is a rare congenital anomaly. There are two alternate exits for coronary venous return: unroofed coronary sinus and persistent left superior caval vein. The coronary venous direction could be bidirectional depending on the pressure balance between the left atrium and the systemic vein. This anomaly has the risk of heart failure, paradoxical embolism, and cyanosis.