Human mesenchymal stromal cells, whether from the bone marrow or adipose tissue (hASCs), are promising cell therapy agents. However, generation of abundant cells for therapy remains to be a challenge, due to the need of lengthy expansion and the risk of accumulating genomic defects during the process. We show that hASCs can be easily induced to a reversible fast-proliferating phenotype (FP-ASCs) that allows rapid generation of a clinically useful quantity of cells in <2 weeks of culture. Expanded FP-ASCs retain their finite expansion capacity and pluripotent properties. Despite the high proliferation rate, FP-ASCs show genomic stability by array-comparative genomic hybridization, and did not generate tumors when implanted for a long time in an SCID mouse model. Comparative analysis of gene expression patterns revealed a set of genes that can be used to characterize FP-ASCs and distinguish them from hASCs. As potential candidate therapeutic agents, FP-ASCs displayed high vasculogenic capacity in Matrigel assays. Moreover, application of hASCs and FP-ASCs in a fibrin scaffold over a myocardium infarct model in SCID mice showed that both cell types can differentiate to endothelial and myocardium lineages, although FP-ASCs were more potent angiogenesis inducers than hASCs, at promoting myocardium revascularization.