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Objective:To investigate the protective effect and mechanism of lithium chloride pretreatment on myocardial ischemia-reperfusion injury(I-RI) in rats.Methods:A total of60SD rats were randomly divided into control group, model group, lithium chloride intervention group and L-arginine methyl ester+ lithium chloride intervention group with15 in each.TheI-RI model was established in model group, the lithium chloride intervention group andL-arginine methyl ester+ lithium chloride intervention group by method of seaming along left anterior descending coronary artery myocardial, control group was only opened the chest without seaming,ST-elevation within2 min was regarded as modeling success.Model group did not adopted any intervention, lithium chloride intervention group was treated with lithium chloride injection 15 mg/kg by jugular venipuncture preoperatively,L-arginine methyl ester+ lithium chloride intervention group was treated with intraperitoneal injection of30 mg?kg-1?d-1L-arginine methyl ester7 d before the test, and intravenous catheter of15 mg/kg lithium chloride preoperatively. The hydroxybutyric acid dehydrogenase(HBDH), creatine kinase isoenzyme(CK-MB), superoxide dismutase(SOD), malondialdehyde(MDA) level and nitric oxide synthase(NOS) activites were tested.Each large area of myocardial ischemia tissue was extracted for determination of the MDA content,SOD activity in tissue and serum, and morphological changes of myocardial tissue.Results:SOD activity was highest in lithium chloride intervention group, followed by L-arginine methyl ester+ lithium chloride intervention group, control group and model group (P<0.05);SOD activity was highest inL-arginine methyl ester+ lithium chloride intervention group intervention group, followed by lithium chloride intervention group, control group and model group(P<0.05).MDA content of myocardial tissue was highest in model group, followed by L-arginine methyl ester+ lithium chloride intervention group, the lithium chloride intervention group and control group(P<0.05); serumMDA content was highest inL-arginine methyl ester+lithium chloride intervention group, followed by model group, lithium chloride intervention group and control group(P<0.05).Compared with the control group, serumNOS was significantly higher in model group, lithium chloride intervention group andL-arginine methyl ester+ lithium chloride intervention group(P<0.05), there was no statistical difference of serumNOS activity between the three groups(P>0.05);HBDH andCK-MB of plasma were highest in model group, followed byL-arginine methyl ester+ lithium chloride intervention group, lithium chloride intervention group and control group(P<0.05).A significantly lighter myocardial damage was observed microscopically in lithium chloride intervention group than that inL-arginine methyl ester+ lithium chloride intervention group and model group.Conclusions:lithium chloride pretreatment can significantly reduce the myocardialI-RI, maintain structure and function of myocardial cells, improve the antioxidant ability of myocardial tissue, play an effective role on protecting myocardialI-RI.