Cor triatriatum is rare congenital cardiac anomaly first described by Church in 1868. The anomaly consists of an abnormal partitioning of the left atrium by a fibromuscular membrane that divides the atrium into an upper chamber, which receives the pulmonary veins, and a lower chamber, which contains the atrial appendage and the mitral valve. The upper and lower chambers communicate through a stenotic fenestration in the membrane, which has the hemodynamic consequence of pulmonary venous obstruction. Recently we experienced cot triatriatum associated with partial anomalous pulmonary drainage to right atrium. The upper chamber was connected to right atrium through a sinus venous type of ASD and received left superior and both inferior pulmonary vein, whereas the lower chamber so called true left atrium communicated with right atrium through foramen ovale type of ASD, left atrial appendage and mitral orifice. And the anomalous membrane has no fenestrations which permit blood flow. The operation was made right atrial approach under the CPB. We excised completely the anomalous septum and reconstructed atrial septal defect with pericardial patch to drain the right upper pulmonary vein to the left atrium. The postoperative course has been good during follow up.