Cor triatriatum in an adult with mitral regurgitation and massive left atrial enlargement.

An unusual case of cor triatriatum in a 52-year-old woman is described in which the preoperative diagnosis was obscured by the presence of mitral valvular regurgitation and massive left atrial enlargement; such massive left atrial enlargement has not been reported before in this entity. Only the right pulmonary veins drained into the accessory chamber. The abnormal septum dividing the left atrium was demonstrated by two-dimensional but not M-mode echocardiography.