OBJECTIVE: To explore the effect of cardiopumlonary bypass using the bloodless priming technique in open-heart surgery in children. METHODS: Fifty cases of atrial septal defect (ASD) or ventricular atrial septal (VSD) were randomly divided into a bloodless priming group (n=25) and a control group receiving blood priming (n=25). The Hct, furosemide dosage, urine output, pericardial and mediastinal drainage, and time of wakening and of mechanical ventilatory support were deternined intraoperatively and postoperatively. RESULTS: The intra and 12 h post operative Hct ［(19.0±6.8) % and (30.4±25.2)%, respectively］ in the bloodless group was lower than that in the blood primed group ［(23.4±10.6)% and (33.2±23.4)%, respectively］ (P<0.05). The intra and post operative doses of furosemide ［(5.2±0.8) mg and (4.5±0.6) mg, respectively］ in the bloodless group were larger than those in the blood primed group ［(1.2±1.0) mg and (1.5±0.5) mg, respectively］ (P<0.05). The intra and 24 h post operative urine output in the blood less group ［(218±56) ml and (278±38) ml, respectively］ was higher than that in the bloodprimed control group ［(78±36) ml and (189±62) ml, respectively］. The Hct did not differ between the bloodless group and bloodprimed group 24 h after the operation ［(38.6±25.2) % vs (38.8±24.3) %］. Pericardial and mediastinal drainage and time of wakening and postoperative mechanical ventilatory support did not differ in the two groups. CONCLUSIONS: Cardiopulmonary bypass using the bloodless priming tecnique appears to be safe and practicable in pediatric openheart surgery procedures.