Objective To establish a new cell resource of stem cell transplantation for heart failure therapy, by using cardiomyocytes from rat marrow mesenchymal stem cells(MSCs). Methods MSCs were isolated and cultured from rat bone marrow, then induced by 5-aza (5, 10, 15, 20 μmol/L) for 24 hours. The cultured cells were observed with phasecontrast microscopy. The immunohistochemical technique and laser scanning confocal microscopy (LSCM) were applied for revealing the expressions of desmin, α-sarcomeric actin and C-TnT. The induced cells were evaluated by a transmission electron microscope. GATA4 and α-MHC expressions were detected by relative quantitative RT-PCR after 7, 21, 28 days of inducement respectively. Results MSCs induced in vitro by 5-aza could be identified by the positive staining for desmin, α-sarcomeric actin and C-TnT. The number of cells stained positively in the 5 μmol/L was greater than that of other groups. Transmission electron microscope showed that paralleled myofilaments were formed. RT-PCR assessment showed that the differentiated cells began to express GATA4 from day 7 to day 28 of differentiation and began to express αMHC from day 21 to day 28 of differenti