Unroofed coronary sinus (coronary sinus-type atrial septal defect) is a rare congenital anomaly resulting from imperfect development of left atrio-venous fold. This malformation is not considered suitable for percutaneous treatment due to complex anatomy and risk of coronary sinus obstruction. This article reports on the first successful treatment of partially unroofed coronary sinus by implantation of an Amplatzer® Septal Occluder device (AGA Medical Co., Golden Valley, MN). In this patient, the malformation was deemed favorable for device closure due to the local anatomy and the association with persistent left superior vena cava draining in coronary sinus. © 2012 Wiley Periodicals, Inc.