Missed unroofed coronary sinus.

Coronary sinus atrial septal defect (ASD) is a rare congenital cardiac anomaly, which might be difficult to diagnose. In this report, we describe a patient with small secundum ASDs and an associated large coronary sinus ASD, which had been missed at initial evaluation. The diagnosis of coronary sinus ASD was established by using transesophageal echocardiography after percutaneous closure of a small secundum ASD at another center. Patient underwent corrective surgery.