A total and consecutive 240 patients operated on using heart-lung machine and cold potassium cardioplegia for their either congenital or acquired heart diseases during the 6-month period between January and June 1981 were reviewed by studying the intraoperative procedures and early postoperative courses. The conduct of extracorporeal circulation were monitored with hemodynamic parameters. The early postoperative management and the clinical data along with the changes of blood gas studies were sum-marized according to the seven groups divided in accordance with disease characteristics. They were: Groups I, Secundum atrial septal defect [15 patients]; II, Pulmonary stenosis [9 patients]; III, Ventricular septal defect [68 patients]; IV, Tetralogy of Fallot [46 patients]; V, Acquired valvular heart disease with valve replacements [79 patients]; VI, Acyanotic other heart diseases [9 patients]; and VII, Cyanotic other heart diseases [14 patients]. The most frequent complications after surgery were ventricular arrhythmia and low outputs. There were 20 deaths postoperatively: 19 patients [7.9%] died within 30 days after surgery and one patient [0.4%] 3 months after operation with overall mortality rate of 8.3% among 240 patients. The mortality rates according to the groups were as follows: Groups I, II and VI, none; III, three early deaths [4.4%]; IV, ten early deaths [21.7%]; V, two early and one late deaths [3.8%]; VII, four early deaths [28.6%]. These clinical results suggested that early surgical risks of open heart surgery were related closely to the intracardiac anatomy rather than the patient`s age and body size. Better clinical results would be expected from planning the reconstructive surgery of the right ventricular outflow tract with care when the hypoplastic pulmonary arteries are present. [KTCS 1982;1:77-89]