BACKGROUND: Present therapeutic tool cannot supplement infarct myocardium. Studies have shown that stem cell transplantation can promote regeneration of myocardium and vessels and improve heart function and prognosis.OBJECTIVE: To observe changes in morphology and hemodynamics in myocardium following embryonic stem cell transplantation in and surrounding the acute myocardial infarct site.DESIGN, TIME AND SETTING: The randomized, controlled, animal study was performed at the Laboratory of Neurobiology,Department of Human Anatomy and Neurobiology, Xiangya Medical College, Central South University from March 2007 to October 2008.MATERIALS: A total of 40 SPF grade Wistar rats were equally randomized into 4 groups, normal control, infarct model,central transplantation and peripheral transplantation groups. Embryonic stem cells-D3 (ES-D3) and Buffalo rat hepatocytas were supplied by Shanghai Cell Institute, Chinese Academy of Sciences.METHODS: Following resuscitation, ES-D3 cells at (2.0-5.0)×107/L were incubated in a flask, and induced to in vitro differentiate in conditioned medium containing Buffalo rat hepatocytes. Except normal control group, rat models of acute myocardial infarction were established by ligating left anterior descending coronary artery in the infarct model, central transplantation and peripheral transplantation groups. At 1 week following model induction, ES-D3 cells were labeled by BrdU for 1 day, and implanted at 1×109/L. Three sites were selected in the infarct site in the central transplantation group. 10 μ L cell suspension (104 cells) was implanted in the ventricular wall through each site. In the peripheral transplantation group, an equal volume of cell suspension was separately implanted in three peripheral infarct sites by the same method.MAIN OUTCOME MEASURES: Results of immunohistochemistry and hemodynamics were measured.RESULTS: ES-D3 cells in buffalo rat hepatocyte conditioned medium presented regular colony-shaped. At 8 days following differentiation, some embryo proper had spontaneous rhythmic contraction, showed positive reaction of cardiac troponin T after immunostaining. Under the electron microscope, myotube and muscle fiber appeared, which verified the differentiation of cardiomyocytes. Cells were positive for BrdU in the peripheral transplantation group, but negative in the central transplantation group. Cells were also positive for cardiac troponin T. 4 weeks following transplantation, left ventricular systolic pressure,minimum/maximum rate of ventricular pressure (±dp/dtmax) were significantly reduced (P ＜ 0.01), but left ventricular end diastolic pressure was significantly increased (P ＜ 0.01), left ventricular mass and left ventricular mass index were significantly increased (P ＜ 0.01 ) in the infarct model group compared with the normal control group. Compared with the infarct model group, no significant changes in hemodynamics indices were found in the central transplantation group (P ＞ 0.05); left ventricular systolic pressure, ±dp/dtmax were significantly increased (P ＜ 0.01), left ventricular end diastolic pressure was significantly decreased (P ＜ 0.01 ), left ventricular mass, left ventricular mass index and infarct area were significantly reduced(P ＜ 0.01) in the peripheral transplantation group.