A damaged heart can be repaired with a dose of stem cells, French researchers have shown. Their study provides the first direct evidence that stem cells injected into an injured heart do develop to take on some of the workload.

Muscle stem cells, called myoblasts, were taken from the thigh muscle of a man who had suffered a heart attack, cultured, and then injected into his heart. The function of the 72-year-old man’s heart was stronger after the treatment.

But it was only when he died 18 months later that researchers could prove that the injected myoblasts had metamorphosed.