An important field resulting from stem cell research is the discovery and application of biochemical signals to direct existing stem cells in the body - they can be made to repair damage where they would ordinarily remain inactive. Only where stem cells themselves are damaged would new cells be needed: in most situations, greater control over the cells you have is good enough. Via Xconomy: "Provasculon is tackling one of the bigger ideas in regenerative medicine - how to stimulate growth of new blood vessels after they've been damaged by a heart attack. ... in rat studies that a novel protein was able to stimulate a certain type of stem cells (better known to scientists as endothelial progenitor cells) to migrate to damaged heart tissue, promote growth of new blood vessels, and ultimately help the heart pump better after a heart attack. The trick here is that Provasculon is trying to make a genetically engineered form of the key protein, SDF-1, that is able to avoid certain enzymes in the body that would like to chop the protein up and render it useless."

Link: http://www.xconomy.com/boston/2008/10/09/provasculon-a-biogen-backed-startup-testing-regenerative-medicine-on-hearts/