BACKGROUND:: Many studies on animals have suggested that bone marrow mesenchymal stem cells (BMSCs) have the potential to transdifferentiate into cardiomyocytes (CMs) within the myocardial environment both in vivo and in vitro. However, few studies in humans are reported in this field and the molecular signals that underlie this process are not fully understood. OBJECTIVE:: To investigate the effects of human myocardial extracts on transdifferentiation of BMSCs and temporal expression of related genes. METHODS:: Human BMSCs were harvested in vitro. Human BMSCs from passage 4 were induced by high level of autologous myocardial extracts for 2 weeks. Cardiomyogenic differentiation was confirmed by phase contrast microscope and immunostaining against a-actin and cardiac troponin-T (cTnT), and reverse transcriptase-polymerase chain reaction (RT-PCR) was performed for temporal expression of related genes Nkx-2.5, GATA-4, MEF-2C, α-MHC and cTnT. RESULTS AND CONCLUSION:: After induced by myocardial extracts, BMSCs showed a stick-like morphology, with a greater volume and stronger three-dimensional sense. 25.53% of BMSCs were positive for a-actin and 23.48% for cTnT at 2 weeks. The expression level of Nkx-2.5, GATA-4 and MEF-2C genes began to increase at 3 days, the expression level of GATA-4 and MEF-2C genes reached a peak at 5 days after induction and remained at relatively high level afterwards, and the expression level of Nkx-2.5 was gradually increased with the induction time. The expression of a-MHC and cTnT genes, which were not detected before induction, began to emerge at 3 days after induction and remained at high level afterwards. Therefore, myocardial extracts are conducive for BMSCs to differentiate into CMs in vitro, along with the temporal expression changes of Nkx-2.5, GATA-4, MEF-2C, α-MHC and cTnT genes during the transdifferentiation.Zeng JY, Wei YF, Wang Y, Xie A, Lou YL, Zhang M.Effects of human myocardial extracts on transdifferentiation of bone marrow mesenchymal stem cells and temporal expression of related genes.Zhongguo Zuzhi Gongcheng Yanjiu yu Linchuang Kangfu. 2010;14(23): 4181–4185. [http://www.crter.cn http://en.zglckf.com]