Objective    To explore the cardiac differentiation of human embryonic stem cells (ESCs) in coculturing with human fetal cardiomyocytes.     Methods    Fetal cardiomyocytes and fibroblasts were obtained from the aborted fetus

and human ESCs were from the inner cell mass (ICM) of the surplus embryos for tube babies

with the treated fibroblast as feeder layer. Human ESCs of passage 2 to 5 were cocultured with fetal cardiomyocytes at the ratio of 1∶2

and the XY chromosome types of these two kinds of human cells were different to each other in order to be marked. At the same time

human ESCs without coculture were used as negative control. The cocultured cells were harvested 5 days later and were double-stained with human XY chromosome probe and cardiac specific antibody (desmin or cardiac troponin I

cTnI).      Results    On coculture day 5

40%-50% human ESCs expressed cardiac specific antigens

and human ESCs without coculture did not express those antigens.     Conclusion    Human ESCs could be induced into cardiac differentiation by the coculture with fetal cardiomyocytes

and hopefully they will be the candidate for cell transplantation of heart.