ScienceDaily notes a growing understanding of how to signal and control stem cell healing processes: "The molecule c-kit is the 'switch' that needs to be turned on by the 'SOS signals' sent by the damaged heart. By binding to another molecule called the stem cell factor - much like a lock and key - the 'turned on' c-kit activates the bone marrow cells to migrate to the heart to help stimulate new blood vessel growth. ... mice with defective c-kit bone marrow cells, could not mobilize these cells to race towards the injured site and regenerate the injured heart. ... The study may explain why some patients have mild heart attacks and others develop progressive and potentially fatal congestive heart failure. ... We know that the number of c-kit positive cells decreases with age and that elderly patients don't recover from heart attacks as well as younger patients. The key for the older patients would be to find new ways to restore this particular subset of cells in their bone marrow."