Abstract: Objective To study the effect of early transplanted bone marrow-derived mesenchymal stem cells(MSC) on apoptosis of myocardial cells,hemodynamics and function of left ventricle(LV) in rats following acute myocardial infarction(AMI). Methods MSC were isolated from Wistar rats by density gradient centrifugation and incubated with adherent culture method.A rat AMI model was established by permanent ligation of the left anterior descending coronary artery.Thirty minutes later,the animals were randomly divided into MSC group(n=10),AMI group(n=10),and sham operation group(n=5).Apoptosis of myocardial cells,hemodynamics and function of LV were monitored by echocardiography and TUNEL 72h after transplantation of MSC. Results The mean arterial blood pressure,left ventricular systolic pressure,left ventricular ejection fraction,and shortened fraction were significantly lower while the left ventricular end diastolic pressure was significantly higher in AMI group than in sham operation group.The rate of cardiac infarction and apoptosis of myocardial cells was 41.6% and 18.9%,respectively,which decreased to 32% and 51%,respectively,after MSC transplantation(P<0.01).However,no significant difference was found in the mean arterial blood pressure,LV systolic pressure,end LV diastolic pressure and LV function between the two groups(P>0.05). Conclusion Early MSC transplantation decreases the apoptosis of myocardial cells but cannot improve the left ventricular function of rats following AMI.