[Cor triatriatum diagnosed in adulthood; report of a case].

Cor triatriatum is a rare congenital cardiac anomaly especially in adulthood. A 68-year-old female was diagnosed as a cor triatriatum classified to Lucas-Schmidt IA, severe degree of mitral regurgitation and atrial fibrillation. Resection of the abnormal diaphragm in the left atrium and miral valve replacement were performed. Although the reason of sudden death of this patient after discharge is unknown, surgical intervention for atrial fibrillation should have performed to prevent a thromboembolism in such cases.