Cor triatriatum with a left upper anomalous pulmonary venous return to the innominate vein.

Cor triatriatum sinister is an uncommon congenital cardiac anomaly accounting for 0.1% of all congenital cardiac malformations, with an anomalous venous return being a frequently associated condition. We present the case of a 14-year-old girl misdiagnosed as having an atrial septal defect with pulmonary hypertension who actually had a cor triatriatum with a left upper anomalous pulmonary venous return to the innominate vein.