Cor triatriatum (CT) is a rare cardiac anomaly, characterized by a membrane in the left atrium which separates the atrium into the proximal and distal chambers. Association of CT with atrioventricular septal defects (AVSD) is extremely rare; only three cases with complete AVSD and 10 with partial AVSD have been reported. In this study, we present an 11-month-old female infant with complete AVSD and cor triatriatum. The patient recovered uneventfully after surgery and normal cardiac performance was achieved 2 years later.