Recent studies revealed that cardiomyocytes can be regenerated from both embryonic- and adult bone marrow-stem cells in animal experiment. Regenerated cardiomyocytes had fetal ventricular phenotype, expressed alpha 1, beta 1, and beta 2-adrenergic, and M2 cholinergic receptors, and revealed spontaneous beating. These cells could be transplanted into the recipient heart, and survive for long period. Clinical application of these cells had some problems at present. Embryonic stem cells had ethical problems, and had a possibility of making teratoma when undifferentiated cells could not be eliminated. Adult stem cells had a difficulty in isolation and culture expansion, since they were not yet well characterized. However, transplantation of regenerated cardiomyocytes would become a future method for the treatment of severe heart failure.