The mechanism(s) of action of implanted stem cells and their regenerative capacity. After implantation in injured tissue, cell survival plays a major role in the repair process. The cell's ability to survive consequently leads to better long-term proliferation, self-renewing ability, and multipotent differentiation capacity, but the main effect within the injured tissue appears to be as a reservoir for secreting molecules that can induce a variety of paracrine effects, especially chemo-attraction. The paracrine effect may have a major influence on the local microenvironment (blocking angiogenesis in articular cartilage) or on the systemic environment that involves the recruitment of host cells from the systemic circulation (increasing angiogenesis in the heart). The systemic effect appears to be primarily involved with angiogenesis, which is responsible for bringing a multitude of stem cells to the injured tissues.