AIM: To investigate the effects of compound salvia miltiorrhiza(SM) injection on lung injury after cardiopulmonary bypass(CPB).METHODS: Twenty-four rats were randomly divided into control group,CPB group and SM group.Cardiopulmonary bypass was made in rats of CPB group and SM group.Lung tissues of all rats were taken 60 min after the weaning of CPB for the assay of malondialdehyde(MDA),myeloperoxidase(MPO),water content of tissue, the observation of pathological changes were made under optical microscope.RESULTS: Remarkable pathohistological and biochemical changes were detected 1 h after CPB.Compared with control group,MDA in lung tissue were increased in CPB group and SM group(P