Open heart surgery without homologous blood transfusion in adults is a generalized method, but not in children and infants. We have attempted to perform open heart surgery without blood transfusion in small children and infants, and report here our experiences and ideas in this regard. The number of open heart surgeries we performed on patients less than 15 years old was 117 from April 1988 to April 1993. In 57 patients among them we attempted open heart surgery with bloodless priming in the cardiopulmonary bypass circuit. Eleven patients were given blood transfusion during the operation or the post-operative period. Another 46 discharged without blood transfusion. From April 1988 to December 1990 (the earlier period) we used the conventional style cardio-pulmonary bypass circuit with gravity venous drainage for 12 patients undergoing open heart surgery without blood transfusion. The lowest weight of these patients was 13 kg and the main diseases were ASD and mild VSD. From January 1991 to April 1993 (the later period), we used the new type cardio-pulmonary bypass circuit with lower priming volume for 34 patients undergoing open heart surgery without blood transfusion. The youngest age was 7 months and the lowest weight was 6.5 kg. The diseases were ASD (9), mild VSD and VSD/PH (15), TOF (6) and other (4). In the new cardiopulmonary bypass system, the venous reservoir and cardiotomy sucker are given negative pressure ((-10)-(-40) mmHg) with a vacuum not a pump, and only one roller pump is used for the arterial pump.(ABSTRACT TRUNCATED AT 250 WORDS)