Background: Vascular endothelial growth factor (VEGF) is well known to induce angiogenesis and cardiac myogenesis after a myocardial infarction. It has been also known that VEGF treatment leads to enhancement of mesenchymal stem cells (MSCs) viability in infarct heart by reducing cellular stress and increasing cell factor. Therefore, it is anticipated that cell therapy using genetically modified MSCs expressing VEGF may offer a potentially valuable approach for the treatment of myocardial infarction due to their enhanced survival and angiogenic capacity. Hypothesis: We hypothesized that hypoxia-inducible VEGF expressing MSCs (HI-VEGF-MSCs) would enhance their own cell survival rate after transplantation, increase neovascularization, and reduce ischemic myocardial injury in a rat model. Methods: Hypoxia-inducible VEGF plasmid was transfected into rat MSCs using a non viral gene carrier, linear polyethyleneimine. In vitro and in vivo VEGF expression level was detected via VEGF ELISA analysis. Fibrosis and infarct size were assessed using Masson���s trichrome staining and TTC staining, respectively. MSCs survival, angiogenic capacity and cardiomyocyte apoptosis were assessed using DAPI staining, anti-CD31 antibody immunostaining and TUNEL assay, respectively. Results: After cell transplantation into the infarted heart, the cell survival rate of HI-VEGF-MSCs was significantly increased compare to intact MSCs. HI-VEGF-MSCs transplantation exhibited great improvement in the degree of cardiac fibrosis in ischemic rat myocardium compare to control groups. The micro-vessel density of the infarcted myocardium was markedly increased in HI-VEGF-MSC-transplanted groups compare to control groups. Infarct expansion was twofold lower in the HI-VEGF-MSC treated group than in the unmodified MSCs-transplanted ones, suggesting that the improved therapeutic effects of the HI-VEGF-MSCs could be caused by their augment neovascularization and cell survival. The extent of cardiomyocyte apoptosis was greatly increased after LAD-ligation. The HI-VEGF-MSC treatment showed greatly reduced cardiomyocyte apoptosis, indicating that the improvement in VEGF expression by HI-VEGF-MSCs could lead to enhance the ability to inhibit cardiomyocyte apoptosis induced by ischemia. Conclusion: We have demonstrated a new approach to cell-based gene therapy using MSCs genetically engineered to overexpress VEGF under hypoxia for the treatment of myocardial infarction in rats.