Objectives To investigate the anti-apoptotic effects of mesenchymal stem cells (MSCs) on hypoxic injured cardiac myocytes in vitro. Methods MSCs were isolated from bone marrow of Sprague-Dawley (SD) rats, and cardiac myocytes from neonatal rats. The rat cardiac myocytes were co-cultured with MSCs or MSC-conditioned media in anoxia (95%N2+5%CO2) for 72 hours. Cell apoptosis was measured by Hoechst 33258 staining. The expression of Bcl-2 and Bax in cardiac myocytes was tested by Western Blot. Results The apoptotic rate was 51.6%±2.4% when cardiac myocytes were cultured in continuous hypoxia and was significantly decreased when cardiac myocytes were cocultured with MSCs or MSC-conditioned media (15.1%±5.4% and 24.0%±4.2% respectively, P<0.001). The decreased expression of Bax in the cardiac myocytes was greatly related to the decreasing of apoptosis, but there was no difference in Bcl-2 expression among these groups. Conclusions Co-cultured MSCs showed significant anti-apoptotic effects on cardiac myocytes in continuous hypoxia. The mechanism may be the interact of cell to cell and paracrine of cytokines which effected the expression of Bax in the cardiac myocytes. Objectives To investigate the anti-apoptotic effects of mesenchymal stem cells (MSCs) on hypoxic injured cardiac myocytes in vitro. The MSCs were isolated from bone marrow of Sprague-Dawley (SD) rats, and cardiac myocytes from neonatal rats. The rat cardiac myocytes were co-cultured with MSCs or MSC-conditioned media in anoxia (95% N2 + 5% CO2) for 72 hours. Cell apoptosis was measured by Hoechst 33258 staining. The expression of Bcl-2 and Bax in cardiac myocytes was tested by Western Blot. Results The apoptotic rate was 51.6% ± 2.4% when cardiac myocytes were cultured in continuous hypoxia and was decreased decreased when cardiac myocytes were cocultured with MSCs or MSC-conditioned media (15.1% ± 5.4% and 24.0% ± 4.2% respectively, P <0.001). The decreased expression of Bax in the cardiac myocytes was greatly related to the decreasing of apoptosis, but there was no difference in Bcl-2 expression among these groups. Conclusions Co-cultured MSCs showed significant anti-apoptotic effect s on cardiac myocytes in continuous hypoxia. The mechanism may be the interact of cell to cell and paracrine of cytokines which effected the expression of Bax in the cardiac myocytes.