Disclosed are human cardiomyocyte progenitor cells (CMPCs) from human heart tissue that are characterised by the Sca-1 or Sca-1 eptiope and CD31 on the cell surface. Further disclosed are methods for ex vivo isolation of CMPCs and differentiation of CMPCs into mature cardiomyocytes using a demethylating agent (5-azacytidine or 5-aza-2-deoxycytidine) and TGF-beta. Further disclosed are pharmaceutical compositions comprising cardiomyocytes for use in cardiomyocyte replacement therapy and for the treatment of myocardial infarction or for ameliorating the effects of myocardial infarction.