The first case of open heart surgery was performed on a ventricular septal defect utilizing a pump-oxygenator in this Department on August 6, 1959. Since the first case 834 open heart surgery cases were done in this Department up to the end of October 1979 during the 21 years period. There were 557 congenital cases, consisting of 296 acyanotic and 261 cyanotic cardiac anomalies. There were 277 acquired heart disease cases, consisting of 266 valvular lesions and several other lesions consisting of 4-atrial myxoma cases etc. In 296 acyanotic cases frequently encountered anomalies were ventricular septal defect [135 cases], atrial septal defect [82 cases], and pulmonary stenosis [26 cases]. In 261 cyanotic anomalies 229 cases of tetralogy Fallot were found. In 266 valvular lesions mitral regurgitation and mitral stenosis were the main lesions, consisting of 98 and 70 cases respectively. There were 226 valve replacement cases including 42 double valve replacement patients. The operative mortality decreased remarkably with increasing cases of open heart surgery recently. In recent years about 10% operative mortality was noted in tetralogy of Fallot, less than 5% mortality in VSD and ASD and mitral valve replacement. In Korea, infant open heart surgery, rare complicated congenital anomalies, and coronary bypass surgery have to be developed in the future. In recent years,Shiley Oxygenator & Ionesque-Shiley pericardial xenograft for valve replacement were utilized mainly in this Department with satisfactory results.[KTCS 1979;4:434-441]