An atrial septal defect (ASD) is a hole in the wall (septum) that separates the two upper chambers (atria) of the heart. The defect allows blood to flow from one atrium to the other, usually from the left side to the right side. ASDs account for 5% to 10% of all coronary heart disease , and for about 30% of the congenital heart defects diagnosed in adults.The operative mortality is < 1% in the absence of significant pulmonary hypertension. Surgical repair in young adults (< 25 years) results in long-term survival rates similar to those of matched controls. Repair in patients older than 40 years does not eliminate the risk of atrial arrhythmias and cerebrovascular accidents.