The hearts of newborn mice can repair themselves after an injury, a discovery that raises fresh hopes for healing damaged hearts in people. Scientists knew that some fish and amphibians could regrow parts of their hearts after major injuries, but there was no good evidence for this in mammals.

In the latest study, US researchers showed that one-day-old mice could regenerate 15% of their heart tissue within three weeks, an ability they lost a week or so after being born. Heart scans showed that parts of the organ that had been surgically removed had not only grown back but were functioning normally.

The finding has raised hopes that the human heart may also have a natural ability to heal itself. If this could be switched on in adults, it could potentially help 750,000 people in Britain alone living with heart damage.

"When a person has a heart attack and heart muscle cells are lost, the heart loses pump function, causing heart failure and eventual death," said Eric Olson, a molecular biologist at Southwestern Medical Centre in Dallas, Texas.