Cor triatriatum sinistrum is a rare congenital cardiac malformation, in which the left atrium (LA) is divided into two distinct chambers by a fibromuscular membrane. Classically, the proximal (upper or superior) chamber of the LA receives pulmonary venous connections, whereas the distal (lower or inferior) chamber contains LA appendage and true atrial septum containing fossa ovalis. The distal chamber is in continuity with the atrioventricular valve, while the two chambers communicate through a defect in the membrane. The hemodynamics of cor triatriatum sinistrum are similar to that of mitral stenosis due to obstructive property of membrane. The majority of reported cases of cor triatriatum occur in infants with symptoms of pulmonary venous obstruction, with adult cases being rare. Herein, we describe an unusual case of cor triatriatum in a 17-year-old boy who presented for the first time with embolic cerebral infarction with left hemiparesis.