Happened to a 38 year old bike racer in the Seattle area years ago (https://recycledcyclesracing.wordpress.com/2009/04/13/brad-l...). I didn't mention him above because it was "cardiac arrest", though I always suspected it was undiagnosed WPW. We're not talking some out-of-shape person thinking they'll run a marathon on no training. No, bike racing is unbelievably hard if you don't want to get dropped and pulled from the race after ten minutes. And Brad was good at it.

So an in-shape athlete in a hard sport at the age of 38 just drops dead mid-race from cardiac arrest? Yeah, I have theories (which, not being a cardiologist, are probably wrong).