RUNNING marathons regularly could leave you with an enlarged heart, scientists have warned.
It was previously thought the aorta was a stable structure with minimal plasticity.
But boffins studying elderly endurance athletes found a quarter had abnormally large aortas.
This could put them at risk of complications such as a leak or rupture.
Massachusetts General Hospital investigator Dr Aaron Baggish said: "It was proof of concept for us because while we'd been seeing it in the clinic for a long time.
"It had never been studied in an isolated fashion.
"We want to know whether this enlargement means the same thing in an athlete as in a non-athlete.
"The first option is that aortic enlargement among master athletes is a benign adaptation and another feature of the so-called athlete's heart, where big is good."
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Dr Baggish added: "If we find that big aortas are a benign adaptation, doctors can be reassured when they see it and not put patients through unnecessary testing and surgery.
"If we find that they really are an indicator of risk, then we have to think about screening people who fit this bill.
"For now, our goal is to alert athletes and their doctors about this evolving story."