Atrial septal defect is the most common of the congenital heart disease in the adult. Since the first description of atrial septal defect by Rokitansky in 1857, this anomaly has been studied by many workers in past one century. In 1953, Lewis had first corrected the atrial septal defect under direct vision with deep hypothermia, and Gibbon [1954] had first done the atrial septal defect under direct vision with extracorporeal circulation. In our college [May 2` 1977], we have first repaired the A.S.D. under direct vision with artificial heart-lung machine and, the defect was 4_5cm in size which was closed by Dacron patch. This patient was 12 year old girl who is well now. [postoperative 13 days][KTCS 1977;1:143-147]