Cor triatriatum sinister with complete membrane and atrial septal defect (ASD) with right-to-left shunt

Cor triatriatum sinister is a relatively rare congenital condition in which the left atrium is bisected by a fibromuscular membrane into two distinct chambers. There are multiple hypotheses for the embryologic origin of this congenital defect. The presentation of patients can be during infancy, childhood, or adulthood, and this is due largely to variation in both the degree of obstruction to pulmonary venous return and the presence of associated lesions. We describe the case of a patient presenting in early adulthood with symptoms associated with cor triatriatum sinister and an atrial septal defect (ASD).