It really is a difficult thing to pinpoint the singular culprit of cardiac arrest but it is increasingly becoming more regular in "young" people. I know of a doctor, same age as me, mid-30's, suffered a heart attack without any prior indications he was likely to. It completely changed how he lived (luckily) after that, to the point of paranoia almost. He watches and counts everything he eats, and he cooks his own meals, and exercises rigorously. He lost a lot of weight and is in better physical shape, and yet it still doesn't mean he's not capable of having another one nor diminished his chances.