Objective To study the protective effects and mechanism of intermittent ventilation on lung injury during cardiopulmonary bypass(CPB). Methods Twenty-four patients with rheumatic heart disease (RHD) were divided into two groups with random number table: treatment group (n=13),given intermittent ventilation once every 5 minutes during CPB; control group (n=11),no ventilation during CPB. Blood samples were obtained preoperatively. A bronchoalveolar lavage was performed at 2 hours after CPB. The numbers of granulocytes, total protein (TP) and tumor necrosis factor-alpha(TNF-α) content in the bronchoalveolar lavage fluids(BALF) were measured, and lung oxygenate index (OI) were measured preoperatively and 1 hour, 4 hours after CPB termination,respectively. Results The numbers of granulocytes, TP and TNF-α content of treatment group in the BALF were significantly lower than those of the control group (Plt;0.01, P=0.02,0.02),and the lung OI of treatment group at 1 hour and 4 hours after CPB termination was also significantly lower than that of the control group(Plt;0.05); a significant increase of lung OI occurred in both groups at 1 hour and 4 hours after CPB when compared with the same group at baseline before CPB(Plt;0.05). Conclusion Intermittent ventilation has the protective effects on lung injury during CPB by decreasing granulocytes adhesion and alleviating lung inflammatory reaction and endothelial cells injury.