Objective To investigate the protective effects of erythropoietin (EPO) on myocardium injury after sepsis in rats in order to clarify the mechanisms.Methods The rat models of sepsis were produced by cecal ligation and perforation method (CLP).Ninty-six healthy SD rats were randomly (random number) divided into 3 groups:the sham operation group (Sham group,n =32),the sepsis group (CLP group,n =32),and the EPO treatment group (EPO group,n =32) treated with EPO 1000 IU/kg intraperitoneal injection after the CLP.The observation intervals were set at 3 h,6 h,12 h and 24 h after the surgery.The cardiac hemodynamics of the CLP group were measured.Plasma levels of inflammatory factors and myocardial enzyme indicators were determined by enzyme-linked immunosorbent assay (ELISA) ; Membrane potential levels of chondriosome of myocardial cells,cell apoptosis rates and expressions of nuclear factor-κB p65 of myocardium tissue were detected by flow cytometer; Then the pathological change of myocardium with HE staining was observed under light microscopy.Results (1) Compared with the CLP group,left ventricle systolic pressure (LVSP),left ventricle diastolic end pressure (LVEDP),the maximum rate of left ventricle rise and fall (+ dp/dtmax and-dp/dtmax) in the EPO group improved (P ＜0.05,P＜0.01); (2) Compared with the Sham operation group,plasma levels of tumor necrosis factoralpha (TNF-α),interleukin-6 (IL-6),C-reactive protein (CRP),cardiac troponin-I (cTNI),creatine kinase (CK),lactate dehydrogenase (LDH) and glutamine-oxaloacetic transaminase (GOT) in the CLP group increased at each interval (P ＜ 0.05),and those biomarkers in the EPO group were lower than those in the CLP group (P ＜ 0.05) ; On the contrary,plasma level of anti-inflammatory factor IL-10 in EPO group was higher than that in the CLP group (P ＜ 0.01) ; (3) Compared with the Sham operation group,the cell apoptosis rates in the CLP group increased significantly (P ＜ 0.01),and it decreased obviously in the EPO group (P ＜ 0.01); (4) Compared with the Sham group,membrane potential levels of chondriosome of myocardial cell in the CLP group decreased (P ＜0.01),while it increased in the EPO group in comparison with the CLP group (P ＜ 0.01) ; (5) Pathological changes of myocardium after the CLP could be lessened by the EPO treatment.Conclusions EPO may increase membrane potential levels of chondriosome and decrease the apoptosis rates of myocardial cell in rats after sepsis,and it may reduced the production of inflammatory factors to protect the myocardial cell by down-regulating NF-κB p65.Both increased membrane potential level of chonriosome and decreased inflammatory factor may implicate in myocardium protection thereby improving cardiac function after sepsis.