ScienceDaily reports on a new study that sheds more light on the way in which stem cells work to regenerate damaged heart tissue. "Most of all, this study is important because it begins to explain why stem cells can help a heart heal. Clinical trials that use bone marrow [adult] stem cells in people with heart damage have shown promise, but no one knows how it works. This starts to provide an explanation. ... human stem cells use different methods to morph into two kinds of cells needed to restore heart function - cardiac muscle cells that contract the heart as well as the endothelial cells that line blood vessels found throughout the organ."