What causes athletes to have sudden heart attacks/cardiac arrest?

Underlying Condition: Most commonly, if this were to happen, an athlete would have an underlying heart condition. What you may be referring to is that long-term athletes can have enlargement of the heart musculature due to increased needs of the body. This could potentially lead to abnormal heart rhythms.

Strctural heart dis: Sudden cardiac arrest is usually due to conduction disease or hypertrophic cardiomyopathy. Pete maravich died of coronary artery disease during a pick up game. It turns out he only had 1 coronary artery. It is the main reason athletes at all levels have preliminary cardiac clearence.