Researchers at Karolinska Institute, a leading medical university in Sweden, have demonstrated that contrary to conventional theory, heart cells are able to regenerate themselves. Examining the heart tissue of 50 people over the course of four years, the researchers found that new heart cells appeared to replace older ones at a rate of approximately 1 percent per year in people in their 20s, falling to 0.5 percent per year by age 75. Scientists now hope to find ways to stimulate this natural regeneration of heart cells as a way to avoid heart transplants and help people recover from heart attacks.