In this study we investigated cardiomyocyte differentiation of rat bone marrow-mesenchymal stem cells (BM MSCs) by treating the stem cells with conditions mimicking that of myocardial infarction. The extract from infarcted rat myocardium Contained the biochemical factors arising after infarction. The cardiac contraction and relaxation were simulated by applying 4% strain at 1 Hz to the stem cells. We found that the extract from infarcted myocardium or 4% strain each alone could induce cardiomyocyte differentiation of BM-MSCs, as shown by expression of cardiomyocyte-specific genes including alpha-actin, connexin 43, Nkx2.5, MEF2c, GATA4, alpha-MHC, and Troponin I. Furthermore, a combination of the extract and 4% strain had stronger effects on cardiomyocyte differentiation than what either treatment alone had. Our results Suggest that this in vitro model system Simulates the local cardiac environment Cues after infarction and may be useful in identifying the biochemical and physical factors involved in cardiomyocyte differentiation. (C) 2009 Elsevier Inc. All rights reserved.