Spurring regeneration by use of signalling molecules is a promising field of medical development. Here is an example from the Technology Review: "scientists have identified a pair of peptides that can stimulate new cell growth and improve heart function in rodents induced to have heart attacks. [Researchers are] now testing one of the peptides, periostin, in pigs induced to have heart attacks. Because these animals have hearts similar in size to humans, they provide a good model for testing new therapies prior to human clinical trials. Preliminary results show that injecting the peptide into the pericardium, the lining around the heart, seems to help. ... [This] approach is, to some degree, in competition with stem-cell therapy, which is already being tested in humans. Scientists are working on different ways of harvesting and delivering stem cells to patients with heart disease, and clinical trials have so far yielded mixed results. Transplanted cells appear to have difficulty surviving and integrating into their new environment. In fact, some scientists suggests that benefit of cell transplants comes from the cells ability to stimulate innate growth. Triggering this process with peptides [may] be a simpler method of treatment of certain conditions such as cardiomyopathy [an enlarged heart] where the problem is lack of viable, contractile heart muscle cells."