The data presented support the utility of VSV-G-mediated fusion to study the effects of stem cell fusion on cell reprogramming and functional improvement of tissues including the heart. Future studies may also employ VSV-G to rescue damaged cells of other ischemic tissues in the body, or even selectively target cells for destruction. For example, the microenvironment of tumors and the overactive osteoclasts in Paget's disease are below the pH threshold necessary to activate the conformational change in VSV-G. Local administration of VSV-G in liposomes containing toxic factors or highly acidic pH to this microenvironment may fuse with these poorly regulated cells and dampen their detrimental effect.