An example of the sort of screening work presently taking place, in China in this case: "Damaged heart tissue is not known for having much inherent capacity for repair. But now, scientists are closing in on signals that may be able to coax the heart into producing replacement cardiac muscle cells. Using a zebrafish model system, researchers have identified a family of molecules that can stimulate stem cells to develop into beating heart muscle cells. ... Despite advances in modern medicine, management of myocardial infarction and heart failure remains a major challenge. There is intense interest in developing agents that can influence stem cells to differentiate into cardiac cells as well as enhance the inherent regenerative capacities of the heart. Developing therapies that can stimulate heart muscle regeneration in areas of infarction would have enormous medical impact. ... The zebrafish is an excellent model organism to study heart growth and development because there are established genetic approaches that permit visualization of fluorescent beating hearts within transparent embryos. After screening nearly 4,000 compounds, the researchers discovered three structurally related molecules that could selectively enlarge the size of the embryonic heart. The compounds, cardionogen-1, -2, and -3, could promote or inhibit heart formation, depending on when they were administered during development. ... Cardionogen opposes Wnt signaling to induce cardiac muscle cell formation. Importantly, the interaction of cardionogen with Wnt seemed to be restricted to specific cell types. ... Evaluating the potential of cardionogen on human adult and embryonic stem cells is the next logical step. This may ultimately aid in design of therapeutic approaches to enhance repopulation of damaged heart muscle and restore function in diseased hearts."