Stem cell transplantation in acute myocardial infarction showed functional improvement of infarcted heart. We hypothesized that myocardial environment in acute myocardial infarction induced differentiation of mesenchymal stem cells (MSCs) into cardiomyocytes. We evaluated the effects of exposure to oscillating pressure and myocardial proteins from infarcted heart, in vitro simulation of in vivo infarcted heart, on differentiation induction of human cord blood derived MSCs into cardiomyocytes. MSCs were exposed to in vitro conditions simulating in vivo environments of beating infarcted heart, as follows;; 1) myocardium derived proteins or serum obtained from rat with sham operation 2) myocardium derived proteins or serum from rats with AMI, with and without application of oscillating pressure. We evaluated differentiation of MSCs with immunostaining and RT-PCR. In RT-PCR analysis, MSCs cultured with normal myocardium derived protein expressed troponin T, GATA4, and ANP weakly, but those with control serum did not. Concomitant exposure to oscillating pressure and myocardium derived proteins induced additional expressions of MHC and connexin 43. Treatment of MSCs with infarcted myocardium derived proteins induced expression of all cardiac specific genes and addition of oscillating pressure augmented these expressions. Dye transfer experiments revealed formation of the functional gap junction between MSCs treated with infarct derived proteins and pressure. Such a differentiation of MSCs was blocked by latecy-associated peptide and noggin, transforming growth factor beta1(TGF-棺1) and bone morphogenic protein-2 (BMP-2 ) blocker. Treatment with TGF-棺1 and BMP2 induced expression of troponin T, connexin 43, and GATA4 and addition of pressure chamber induction of 慣-MHC. We finally confirmed that TGF-棺1 and BMP-2 were elevated in infarcted myocardium by immunocytochemistry and ELISA. These results suggested that infarct-related biochemical and mechanical factors are important in differentiation of MSCs to cells with cardiomyocyte phenotype and TGF-棺/BMP-2 are essential in this process.