I'd like to know if he had a family history of heart problems. That's often the
#1 indicator. You need to pick your parents well.
Having said that, I had a heart attack in 2000 at age 46. It happened while riding my bike doing a 100% max effort racing my daughter up a steep long hill. My family history has no heart problems and I had no prior symptoms. Fortunately it was just one tiny artery and none of the big, bypass types. They can't even get to mine to do a stent so I just live with it and set my heart rate monitor to start beeping at 160 BPM and take a beta blocker. My diet isn't anywhere near perfect, but pretty good.