OBJECTIVE: Infants are usually subjected to serious complications after cardiac surgery with cardiopulmonary bypass (CPB). This study was conducted to evaluate the effects of a modified ultrafiltration technique (MUF) on infants undergoing cardiac surgery with CPB. METHODS: A total of 261 infants less than 1 year old with congenital heart disease and who required CPB were randomized into receive MUF during CPB (n=205) or not (n=56, control group). Bypass duration, aortic cross-clamp duration, postoperative blood effluents and transfusions, mechanical ventilation duration following operation, and hematocrit and oxygenation index 24 hrs postoperatively were compared between the two groups. RESULTS: No ultrafiltration-related complication was found in the MUF group. There were no significant differences in the duration of bypass and aortic crossclamp between the two groups. Postoperative blood effluents and transfusions in the MFU group were significantly reduced (79.5±18.6 mL vs 57.3±15.4 mL and 78.1±32.5 mL vs 67.9±25.6 mL respectively) compared with the control group (P<0.05). The duration of mechanical ventilation following operation in the MFU group was shorter than that in the control group (28.6 ± 9.1 hrs vs 32.3 ± 8.7 hrs; P<0.05). MUF produced a significant improvement in hematocrit (34.6 ± 3.7 min vs 29.8±2.8 min; P<0.01) and oxygenation index ( 275.2±39.1 vs 202.2±25.6; P<0.01) 24 hrs postoperatively when compared with the control group. CONCLUSIONS: MFU can reduce postoperative bleeding and blood transfusions, improve pulmonary function and shorten the duration of mechanical ventilation in infants undergoing cardiac surgery with CPB.