Abstract: Mesenchymal stem cells are pluripotent cells capable of differentiating into myocardial and vascular endothelial cells. The present invention demonstrates that the mesenchymal stem cell sheet have therapeutic potential for a severely damaged heart due to its pluripotency and in situ self-renewal capability. Mesenchymal stem cells derived from adipose tissue were cultured to prepare a mesenchymal stem cell sheet. Four weeks after induction of myocardial infarction in rats, the mesenchymal stem cell sheet was transplanted to the heart. The mesenchymal stem cell sheet were readily engrafted to the surface of the scarred myocardium, grew gradually in situ, and formed a thick layer (approximately 600 ?m) in 4 weeks. The grown transplanted mesenchymal tissue contained newly formed blood vessels, myocardial cells, and undifferentiated mesenchymal cells.