[Cor Triatriatum Diagnosed in Adulthood;Report of a Case].

A 64-years-old man had cor triatriatum (Lucas-Schmidt type I A) with severe mitral regurgitation and atrial fibrillation. We perfomed resection of the anomalous septum between the accessory chamber and left atrium, and conducted mitral annuloplasty and maze procedure. Arrhythmia were not encountered after surgery.