Objectives: To compare the effects of three ventilation strategies during cardiopulmonary bypass on postoperative pulmonary complications (PPCs). Design: A prospective, randomized, double blinded study. Setting: Single center hospital. Participants: forty eight pediatric patients undergoing elective repair of congenital heart diseases with cardiopulmonary bypass. Interventions: Patients were randomly assigned into three groups according to ventilation strategy during CPB: (1) low tidal volume (LTV), RR 5 breath ber min, and Vt 2 -3mL/kg of ideal body weight, (2) continuous positive airway pressure (CPAP) of 5-10 cm H2O, (3). no ventilation (NOV). Measurements: and Main Results: postoperative atelectasis. Regarding the frequency of postoperative atelectasis there was statistically insignificant between the studied groups although the number of patients who developed atelectasis in NVgroup 7 (43.8%) were greater than the number in both LTV group 2 (12.5%) and CPAP group 2 (12.5%) Conclusions: Maintaining ventilation during CPB can reduce the incidence of PPCs in pediatric patients undergoing cardiac surgery.