Embryonic stem cells are pluripotent cell lines that are derived from the blastocyst-stage early mammalian embryo. These unique cells are characterized by their capacity for prolonged undifferentiated proliferation in culture while maintaining the potential to differentiate into derivatives of all three germ layers. During in vitro differentiation, embryonic stem cells can develop into specialized somatic cells, including cardiomyocytes, and have been shown to recapitulate many processes of early embryonic development. The present review describes the derivation and unique properties of the recently described human embryonic stem cells as well as the properties of cardiomyocytes derived using this unique differentiating system. The possible applications of this system in several cardiac research areas, including developmental biology, functional genomics, pharmacological testing, cell therapy, and tissue engineering, are discussed. Because of their combined ability to proliferate indefinitely and to differentiate to mature tissue types, human embryonic stem cells can potentially provide an unlimited supply of cardiomyocytes for cell therapy procedures aiming to regenerate functional myocardium. However, many obstacles must still be overcome on the way to successful clinical utilization of these cells.