Distance runner Ryan Shay collapsed and died will runing in the U.S. men’s marathon Olympic trials. Ryan Shay had an enlarged heart which helped with endurance but it could be the very thing which brought about the tragedy.

“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.

Read more: Elite runner dies at Olympic Marathon Trials