A reminder from the Technology Review that for all the speed of modern stem cell science, turning knowledge into new therapies is a slower process; the devil is in the detail and the regulation. "It's a tantalizing thought: injecting stem cells isolated from a person's own blood into an ailing heart in hopes of repairing years of accumulated decay. But so far, human trials testing cell therapies for heart attacks have yielded mixed results, creating controversy over various aspects of the treatment: the types of cells that are used, the way they are delivered, and when in the course of the disease they are given. With the next round of trials, scientists hope to nail down the precise set of conditions needed to effectively heal a sickly heart. ... In terms of the clinical testing of stem-cell therapies, heart disease is arguably the furthest along of the common diseases. But cell-based therapies are proving trickier to test than traditional drugs and medical devices are. They seem to require the perfect combination of ingredients and execution. Scientists must determine the best cells to transplant, the best way to prepare cells, and when and how they should be delivered."