His large heart meant extra endurance and turned him into an outstanding marathon runner.
But when US marathon runner Ryan Shay collapsed and died Saturday during men's marathon Olympic trials at New York, it was also attributed to his heart problem.
"The thing that made him such a great runner may have killed him," Ryan’s father Joe Shay said.
Ryan and other top athletes underwent medical testing in Flagstaff, Arizona, where he trained, last spring, Joe Shay said, and he was cleared for running.
"He said the doctors told him that because your heart rate is so low, when you're older you may need a pacemaker to make adjustments on that," said Joe Shay, adding his son first was diagnosed with a larger than normal heart at age 14.
Scientists long have noticed the phenomenon of the "athlete's heart." Athletes who train hard in aerobic sports, such as cycling, running or swimming, tend to have a bigger heart that pumps more blood throughout the body.
The 28-year-old Ryan Shay collapsed about 5 1/2 miles into the race that would stretch another 21 miles.
"I got a call that Ryan had fallen down ... then I got another call that his heart had stopped," Joe Shay said.
The medical examiner's office said an autopsy will be performed Sunday.
"It's a big loss for the running community," said 2004 Olympic women's marathon bronze medalist Deena Kastor, who used to train with Shay in California. "It's a day we should be celebrating. It has cast a pall."