Betterhumans reports on attempts to understand how adult stem cells from bone marrow have worked as a therapy for heart damage in some studies. "We set out to confirm, using more stringent criteria, the very appealing strategy of using stem cells from bone marrow to regenerate cardiac muscle, but we found that they never become normal, mature muscle cells. It's clear that the transplanted cells aren't growing, as we once hoped, into heart cells. But they may stimulate growth of new blood vessels into the damaged regions or they may secrete growth factors that promote recovery." Early stage regenerative medicine is moving fast - I expect to see these sorts of questions answered in the next few years.