In 7th grade a student died after running the fields, about a mile. He was the last guy in at 12 minutes or so. I was slow at around 8 minutes as I hated running distance, so I hung with the slackers. His heart had an undiagnosed heart defect. One of the walls of his heart burst. He was literally DRT.
Pete Maravich dropped dead after a pickup game because he was born without a left coronary artery, and his right artery had enlarged to compensate, until it burst.