BACKGROUND AND OBJECTIVES: To explore the lung-protective effect of levosimendan (LS) during cardiopulmonary bypass in a canine model by determining the wet/dry weight (W/D) ratio of lung tissue, malonaldehyde (MDA) and superoxide dismutase (SOD) concentrations, and performing a histological evaluation. MATERIALS AND METHODS: Thirty-two canines were divided randomly into four groups and underwent a routine aortic cross-clamping cardiopulmonary bypass procedure for 1 h, followed by recovery for 2 h. Animals were handled as follows: group C (means control group), no special treatment after aortic cross clamping; group P (means pulmonary artery perfusion group), pulmonary artery perfusion with cold oxygenated blood after aortic cross clamping; group LSIV (means intravenous injection of LS group), intravenous injection of LS (65 µg/kg) before thoracotomy, and the rest of the procedure was identical to the control group; group LPS (means pulmonary perfusion with LS group), pulmonary perfusion with cold oxygenated blood combined with LS (65 µg/kg) after aortic cross clamping. Lung tissues were removed and subjected to evaluation of pathological alterations, W/D ratio and MDA and SOD concentrations. RESULTS: In group C, the W/D ratio and MDA concentration were higher, while the SOD concentrations were lower (p<0.05). Compared with groups P and LSIV, the MDA concentration was lower in group LPS, while that of SOD was higher (p<0.05); Light and electron microscopy indicated that LS intervention reduced impairment of lung tissues. CONCLUSION: Our findings suggest that LS plays an important role in protecting lung tissues.