Objective This study was to evaluate the protective effect of pulmonary perfusion with cold modified low- potassium dextran (LPD) solution on lung function after cardiopulmonary bypass in combined aortic and mitral valve replacement. Method Twenty-four consecutive adult patients with combined aortic and mitral valve disease were divided into a control group ( n =14) and a perfused group ( n = 10). Cold modified LPD solution was infused to the main pulmonary artery in the protective group. PaO_2/FiO_2 were monitored at six different time points; preoperation, 0 hour, 1 hours, 2 hours, 6 hours and 12 hours after the termination of CPB. Concentrations of interleukin-6 and interleukin-10 in plasma were measured at four different time points; preoperation, 0 hour, 6 hours, and 12 hours after the termination of CPB. Result PaO_2/FiO_2 in the perfused group were increased more than that in the control group. The IL-6 and IL-10 increased in both groups after operations( P <0. 05). Patients of the perfused group showed significantly reduced IL-6 expression, compared with the control group ( P <0. 001), but the rising extents of IL-10 in the perfused group were higher than that in the control group ( P <0.001). Conclusion Pulmonary artery perfusion with cold modified LPD solution during cardiopulmonary bypass relieved lung injury in combined aortic and mitral valve replacement.