Backgrounds: Transplantation of adult bone marrow-derived mesenchymal stem cell (MSC) has the potential to treat the cardiac repair following myocardial injury. However, poor cell viability after transplantation has limited the regenerative capacity of these cells in vivo. In this study, we transduced heat shock protein (Hsp) 70 into mesenchymal stem cells using Hsp70 fused protein transduction domain (PTD) TAT ex vivo to enhance survival of these cells at the hypoxic conditions in vitro and in vivo. Methods and Results: After 2 weeks culture, MSCs formed colonies with fibroblast-like morphology, over 95% expressed CD71. Recombinant Hsp70-TAT fusion protein was generated by recombination Hsp70 gene with TAT-HA plasmid. Hsp70-TAT fusion protein treated MSCs displayed higher viability than that of control MSCs after 24hrs hypoxia and it was increased at the dose dependently up to 1uM. At hypoxic conditions, Hsp70 transduced MSCs displayed increase of Bcl2/Bax ratio and reduction of JNK phosphorylation, compared to MSCs only. Caspase-3 activity was reduced in Hsp70 transduced MSCs at hypoxic conditions. Besides Hsp70 transduction displayed suppressive effect on cellular ATP depletion at hypoxic condition. After implantation of TAT-Hsp70 transduced MSCs into infarcted myocardium, viable cells labeled with 4���,6-diamidino-2-phenylindole (DAPI) were identified in host myocardium in 4 weeks. The expression of cardiac troponin T (CTn T) and voltage-gated Ca2+ channel (CaV2.1) was increased. Conclusions: Our studies indicate that Hsp70 transduced MSCs enhance cell viability at hypoxic condition in vitro and in vivo. These data may provide genetic modification of MSCs with a therapeutic gene before transplantation as novel therapeutic rationales for the treatment of myocardial infarction and end-stage cardiac failure.