Tehran University of Medical Sciences The Research in Heart Yield and Translational Medicine (RHYTHM) 3115-7270 6 2 2011 06 15 85 88 Afsoon Fazlinezhad Mashhad University of Medical Sciences, Ghaem Hospital Mashhad, Iran. Farveh Vakilian Mashhad University of Medical Sciences, Ghaem Hospital Mashhad, Iran. Asadollah Mirzaei Mashhad University of Medical Sciences, Ghaem Hospital Mashhad, Iran. Azadeh Fallah Rastegar Mashhad University of Medical Sciences, Ghaem Hospital Mashhad, Iran. 2015 10 03 Cor triatriatum  sinistrum is a rare congenital cardiac malformation, accounting for about 0.1-0.4% of all congenital heart diseases and characterized by the presence of a fibromuscular membrane that subdivides the left atrium into two chambers in the classical form. While classic cor triatriatum in most patients can be observed during the neonatal period or early infancy, it is very rare in adults. We herein present an incidental finding of cor triatriatum sinistrum in a middle-aged man with coronary artery disease scheduled for coronary artery bypass graft surgery. The patient was admitted for exertional dyspnea and chest pain of a three-month duration. He had a past medical history of mild hyperlipidemia and mild hypertension. Transthoracic two-D echocardiography (TTE) demonstrated a visible presence of a membranous band in the mid portion of the left atrium with obvious obstruction by color and Doppler flow measurements, confirmed by three-D echocardiography. Selective coronary angiography also revealed a severe ostioproximal stenosis of the left anterior descending artery of up to 99%. On-pump coronary artery bypass grafting was performed without complications, during which the anastomosis of the left internal mammary artery to the left anterior descending artery and the removal of the membrane were done. https://jthc.tums.ac.ir/index.php/jthc/article/view/206 https://jthc.tums.ac.ir/index.php/jthc/article/download/206/204