The present invention provides Jagged 1 and Frizzled 4 as cell surface markers for isolating human cardiomyogenic ventricular progenitor cells, in particular progenitor cells that preferentially differentiate into cardiac ventricular muscle cells. Thus, the invention provides human ventricular progenitor (HVP) cells. The invention provides in vitro methods of the separation of Islet 1+ Jagged 1+ ventricular progenitor cells and/or Islet 1+/Frizzled 4+ ventricular progenitor cells and/or Islet 1+/Jagged 1+/Frizzled 4+ ventricular progenitor cells, and the large scale expansion and propagation thereof. Large clonal populations of isolated Jagged 1+ and/or Frizzled 4+ventricular progenitor cells are also provided. Methods of in vivo use of Jagged 1+ and/or Frizzled 4+ ventricular progenitor cells for cardiac repair or to improve cardiac function are also provided. Methods of using the Jagged 1+ and/or Frizzled 4+ ventricular progenitor cells for cardiac toxicity screening of test compounds are also provided.