Human embryonic stem (HES) cells can give rise to cardiomyocytes in vitro. However, whether undifferentiated HES cells also feature a myocardial regenerative capacity after in vivo engraftment has not been established yet. We compared two HES cell lines (HUES-1 and I6) that were specified toward a cardiac lineage by exposure to bone morphogenetic protein-2 (BMP2) and SU5402, a fibroblast growth factor receptor inhibitor. Real-time polymerase chain reaction (PCR) revealed that the cardiogenic inductive factor turned on expression of mesodermal and cardiac genes (Tbx6, Isl1, FoxH1, Nkx2.5, Mef2c, and α-actin). Thirty immunosuppressed rats underwent coronary artery ligation and, 2 weeks later, were randomized and received in-scar injections of either culture medium (controls) or BMP2 (±SU5402)-treated HES cells. After 2 months, human cells were detected by anti-human lamin immunostaining, and their cardiomyocytic differentiation was evidenced by their expression of cardiac markers by reverse transcription-PCR and immunofluorescence using an anti-β myosin antibody. No teratoma was observed in hearts or any other organ of the body. The ability of cardiac-specified HES cells to differentiate along the cardiomyogenic pathway following transplantation into infarcted myocardium raises the hope that these cells might become effective candidates for myocardial regeneration. ©AlphaMed Press.