This invention provides a method of treating a disorder of a subject's heart involving loss of cardiomyocytes which comprises administering to the subject a composition comprising an amount of a human stromal derived factor-1 and an amount of a human granulocyte-colony stimulating factor, the composition being administered in an amount effective to cause proliferation of cardiomyocytes within the subject's heart so as to thereby treat the disorder. This invention also provides a method of treating a subject suffering from a disorder of a tissue involving loss and/or apoptosis of cells of the tissue which comprises administering to the subject a composition comprising an amount of an agent which induces phosphorylation and/or activation of protein kinase B, or an agent which induces phosphorylation and/or activation of an extracellular signal-regulated protein kinase, or an agent which induces activation of CXCR4.