In 28 children with congenital cardiac lesions, open heart surgery was attempted without homologous blood transfusion using extreme hemodilution for cardiopulmonary bypass (CPB) and moderate to profound hypothermia. The entry criteria for this study were preoperative hemoglobin value above 10 g/dl and expected CPB time of less than 120 minutes. Acyanotic heart diseases such as ventricular or atrial septal defect were the main lesion, but some cases of tetralogy of Fallot and single ventricle were also included in this study. Intraoperative saving of autologous blood and autotransfusion using cell saver were carried out in a part of the subjects. Acceptable lowest values for hemoglobin was 4-5 g/dl and 40% for mixed venous oxygen saturation. As the results, 18 patients tolerated CPB without transfusion and eventually 16 patients were discharged without transfusion at all. The body weight for those without transfusion was 13.9 kg in average and the lowest was 6.8 kg. The significant factor affecting the needs for homologous blood transfusion was prolonged CPB time over 120 minutes. Although there was a tendency that the patients with body weight less than 15 kg received transfusion more frequently than those with body weight more than 15 kg, the body weight was not necessarily a limiting factor. Pre-CPB blood saving and intraoperative autotransfusion were the positive factors for successful non-transfusion open heart surgery.