OBJECTIVE To study the protective effect of exogenous pulmonary surfactant (PS) on respiratory insufficiency after cardiopulmonary bypass in children. METHODS 24 children of VSD associated with pulmonary hypertension undergoing heart surgery with cardiopulmonary bypass(CPB) were randomly divided into two groups: control group and PS group. In the PS group, exogenous natural porcine PS 150 mg/kg was dropped into the intracheal tube before opening the chest and removing the aortic clamp. Equal amount of normal saline was given in the control group. Lung dynamic compliance and oxygenate index were measured before and after operation. The plasma molondialdehyde(MDA) concentration of the lung was analysed perioperatively with ELISA methods. The intubation time of the two groups and ultrastructure of the lung also was measured. RESULTS The dynamic compliance of the PS group was higher than that of the control group (P < 0.05), and the oxygenate index was significantly lower than that of the control group (P < 0.01) after CPB. Compared to the control group, the exogenous PS was able to markedly reduce the generation of MDA(P < 0.01). The intubation time of the PS group was 8.9 hours, much shorter than 13.8 hours of the control group(P < 0.001). The histological examination confirmed that the degree of pulmonary damage was significantly ameliorated in the PS group. CONCLUSIONS Exogenous natural PS has protective effect on respiratory insufficiency after CPB in children with VSD associated with pulmonary hypertension.