Regular and strenuous exercise can repair damage caused by a heart attack, say researchers.
The findings of the new study suggest that damage from heart disease or failure could be at least partially repaired through 30 minutes of running or cycling a day.
Researchers have found for the first time that regular and strenuous exercise can make dormant stem cells in the heart spring into life, leading to the development of new heart muscle.
Scientists had already discovered that stem cells could be coaxed into producing new tissue through injections of chemicals known as growth factors, but the new study is the first to suggest that a simple exercise programme has a similar effect.
An early-stage study on healthy rats showed that an equivalent amount of exercise resulted in more than 60 percent of heart stem cells, which are usually dormant in adults, becoming active.
After two weeks of exercise the mice had a seven percent increase in the number of cardiomyocites, the "beating" cells in heart tissue.
The team from Liverpool John Moores University said that they would now study the effects on mice which had suffered heart attacks to determine whether it could have an even greater benefit.
"The exercise is increasing the growth factors which are activating the stem cells to go on and repair the heart, and this is the first time that this potential has been shown," the Telegraph quoted study leader Dr Georgina Ellison as saying.
"We hope it might be even more effective in damaged hearts because you have got more reason to replace the large amount of cells that are lost," Ellison added.
The study has been published in the European Heart Journal.