Till June 1988, We experienced 3 cases of single atrium at Dept. of Thoracic k Cardiovascular Surgery of National Medical Center. Case 1 was 26 years old female, and had single atrium associated with partial cleft in mitral anterior leaflet and PAPVC. Atrial septation with Dacron patch and MVR [I-S, 31 mm] were done, followed by TAP, De Vega. Postoperative course was good, OPD follow-up for about 4 years with normal physical activity and ordinary working. Case 2 was 4 years old female with single atrium alone. Atrial septation with pericardial patch. Good postoperative course and OPD follow-up for about 2 years with appropriate physical growth. Case 3 was 22 years old female, single atrium with complete cleft in the anterior and posterior mitral leaflet, and septal tricuspid cleft were identified. Atrial septation with polystan bovine pericardial patch and repair of mitral anterior cleft. Postoperatively, residual regurgitation of mitral and tricuspid valve, but tolerable in some limitation of physical activity.