Scientists in the United States have found newborn mice can re-grow their own hearts. The mice had a large chunk of their heart removed a day after birth, only for the heart to restore itself within three weeks. Fish and amphibians are known to have the power to re-grow heart tissue, but the study in Science is the first time the process has been seen in mammals. The study suggests mammals also have such capacity for self-repair, if only for a limited time after birth. There's no reason to believe that the same window would not exist in the human heart.