A new finding in heart regeneration could lead to more effective treatments for heart disease. The study at the University of Cambridge and the University of Washington showed that injecting a mixture of cardiac muscle cells plus epicardial-derived cells enhanced heart regeneration in rats. A Nature Biotechnology paper says the mixture built larger muscle grafts with better blood vessels compared to either cell type alone. This markedly enhanced cardiac function. The epicardium is the outer, protective layer of the heart wall. Its cells play a role in heart development and later in injury response.