Comment by Supermancho

Gaining a ton of body mass working out thickens the heart. It's necessary to push the blood into veins that get constricted, more and more with increased weight. In the epilogue, as you get older, optimal function fades. The thickened tissue isn't as elastic, compounding cardiac problems and sometimes causing infarction (also, not infectious related). Ironically, a thickened heart gives you better odds at surviving surgery, due to the excess tissue and the minimal effect of scarring already-rigid tissue.

Some people see heart walls thinning at a very ripe age (90s+) but for most early heart patients, they don't make it that far.