It's the kind of scene you'd expect in a thriller by Michael Crichton or Robin Cook. A scientist throws some nondescript cells into a lab dish, leaves them alone for a bit and returns to find a disembodied heart thumping away.
That's not quite what's happening in Roger Pedersen's lab at the University of California in San Francisco--at least not yet. But he has managed to turn a group of carefully tended progenitor cells into a patch of thriving, beating cardiac muscle. "It's amazing," Pedersen says, "when you put unspecialized cells away, come back after the weekend and there's a clump...