Abstract: Objective To test the feasibility and safety of autologous bone marrow mesenchymal stem cell (MSC) transplantation by intracoronary injection in acute myocardial infarcted pig (AMI). Methods Coronary occlusion with balloon was used to produce AMI.Labeled MSCs were implanted by intracoronary injection.Four weeks after AMI,single photon emission computed tomography was used to evaluate the relative infarct size,myocardial perfusion score and ejection fraction (EF) of the animals. Left ventricular systolic pressure( LVSP), left end-diastolic pressure (LVEDP), peak rate of pressure rise(+dP/dt) and peak rate of pressure fall (-dP/dt) were assessed by catheterization. Immunofluorescence was performed to evaluate MSC engrafment and differentiation. Results Compared with control group, heart function parameters were all improved in pigs receiving MSCs transplantation, including EF [（44.1±4.3）% vs (39.0±5.2)%, p<0.05] perfusion score （30.0±5.3 vs 41.8±8.8, p<0.01）, relative infarct size[（28.6±4.7）% vs (33.5±3.4)%, p<0.05], LVSP（87.1±8.7mmHg vs 78.0±4.4 mmHg, p<0.05）, +dP/dt（1818.1±116.7mmHg/s vs 1610.6±114.5 mmHg/s, p<0.01） , -dP/dt（1800.9±88.5mmHg/s vs 1618.4±65.7 mmHg/s, p<0.01） and LVEDP（9.4±1.7mmHg vs 12.6±2.8 mmHg, p<0.05）. MSCs implanted in myocardium were stained positively for myosin heavy chain, connexin 43, smooth muscle actin and von Willebrand factor. Conclusions Transplantation of MSCs could improve cardiac function in AMI pig, and that the improvement might result from myocardial regeneration and angiogenesis by MSC differentiation.