Hemorrhage is an important complication after operation with cardiopulmonary bypass and sometimes necessitates a further emergency operation. Between July, 1962 and June, 1985, reoperation for hemorrhage was carried out on 81 patients [3.1%] out of a total 2634 patients who had previously undergone cardiopulmonary bypass surgery at the Department of Thoracic and Cardiovascular Surgery, Yonsei University Medical Center. There were 38 males and 43 females, with an average age of 25 years [ranging 6 months to 60 years] and an average body weight of 38 kg [ranging 5 to 77 kg].There were 43 patients of cyanotic heart disease, 32 patients of acquired valvular heart disease, 4 patients of coronary artery occlusive disease, 2 patients of ascending aorta aneurysm and annuloaortic ectasia. The average amount of blood loss in the case of cyanotic heart disease was 71.7140ml/kg, in acyanotic heart disease 45.16.3ml/kg, in acquired heart disease, 56.514.4ml/kg and in coronary artery occlusive disease, 50.618.7ml/kg during first post operative day. But there was no statistical difference [p>0.05]. The mean blood loss below 10 years old was 70.412.1 ml/kg. Those below 10 years old were believed to bleed more than any other group. But there was also no statistical difference [p>0.05]. Indications for reoperation were continued excessive blood loss [74%], cardiac tamponade or hypotension [23%] and radiological evidence of a large hematoma in the thorax and pericardium [2%]. Average bypass time was 2.10.1 hours [ranging 30 minutes to 5 hours]. The interval between operation and reoperation was as follows; less than 12 hours in 49 patients [60%], 12 to 24 hours in 20 patients [25%], 24 to 48 hours in 8 patients [10%], more than 48 hours in 4 patients [5%]. The commonest sites for bleeding were chest wall [36%], heart [34%], aorta [12%], pericardium [6%], thymus [5%] and others [6%]. But no definite source was found in ll patients [31%]. Twenty seven out of 81 patients [31%] had wound problems and 5 patients [6%] were expired. [Mean SEM]. In conclusion, in order to decrease the amount of blood loss after open heart surgery with cardiopulmonary bypass, shortening of bypass time and bleeding control at the wire suture site during chest wall closure were important. If the amount of blood loss was over 45 ml/kg or 8 m/kg/hour, reoperation should be considered as soon as possible. After operating, careful wound dressings were applied to prevent wound problems.