The fittest people could be wrongly diagnosed as having heart disease because their hearts have become enlarged through frequent exercise, a study suggests.
Scientists knew that the hearts of athletes could grow because of excessive training but did not believe the same effect could happen in amateurs.
Now Imperial College has proved that even people who exercise for as little as an hour three hours a week could be increasing their heart muscle.
While a larger stronger heart is beneficial for keeping up fitness levels it may be confusing doctors into thinking that patients are suffering from heart problems, because a diseased organ also appears swollen and enlarged on scans.
"It's well known that the hearts of endurance athletes adapt in response to exercise, a phenomenon called 'athlete's heart'," said Declan O'Regan, of the Medical Research Council Clinical Sciences Centre, at Imperial.