Eleven infants and children with a body weight of less than 10 kg (median weight, 6.8 kg) whose parents were Jehovah's Witnesses underwent repair (n = 10) or palliation (n = 1) of congenital heart defects without the use of blood products and with (n = 9) or without (n = 2) cardiopulmonary bypass (CPB). In 1 neonate (weight, 3.2 kg) with critical aortic stenosis, moderate hypothermia and a 3.5-minute period of inflow occlusion and circulatory arrest allowed an aortic valvotomy; in another patient (weight 7.0 kg) with tricuspid and pulmonary atresia, transposition of the great arteries, and persistent left superior vena cava, a bilateral bidirectional cavopulmonary shunt procedure was performed without CPB. Use of heparin-bonded tubing allowed reduction of the initial dose of heparin sodium to 1 mg/kg. Tissue perfusion and oxygenation on bypass were adequate, as evidenced by a mean lowest pH of 7.38 +/- 0.09 and a mean lowest venous oxygen tension of 65.0 +/- 36.2 mm Hg. Although the mean postoperative hematocrit (Hct) was lower than the mean preoperative Hct (p < 0.05, analysis of variance and Scheffe's F test), the Hct within 2 hours after CPB was restored to a value (mean Her, 27.5% +/- 1.0%) between the preoperative Hct (mean value, 42.7% +/- 3.5%) and the lowest Her on CPB (mean value, 18.4% +/- 1.4%). The Her at discharge was 31.8% +/- 1.1%. The median postoperative blood loss was 9 mL/kg. There was no perioperative mortality. The median stay in the intensive care unit and the hospital was 2 days and 6 days, respectively. We conclude that repair of congenital heart defects with the use of CPB can be safely conducted in select infants with a body weight of 5 kg or more. In symptomatic neonates or infants with a lower body weight, initial palliative procedures circumvent the use of CPB and allow secondary correction of the defect at a later time.