The atrial septal defect of ostium primum type with cleft anterior mitral leaflet is a rare congenital cardiac defect. It contributes for about 4% of congenital heart diseases and occurs in 2 in 10000 live births. A 12 year old girl’s echocardiography showed this anomaly when the patient presented with breathlessness to the Department of Radiology, Chettinad Medical College and Research
Institute, Chennai. This study focuses on the anatomical knowledge along with embryologic development of inter atrial septum and  endocardial cushions which provide the basis for better understanding of pathophysiology and clinical manifestations of this rare anomaly.