Bodybuilding and Heart Attack

Hi everybody!
I am for several years in bodybulding and I have read quite a lot on nutrition and training. But one thing stays unclear and I didn’t find anything about it in professional sport books. One guy I knew and some other guys that my friends knew had heartattack immediately after or during the weight training in the gym. If I am not wrong Schwartzenegger had several heart interventions?
Does anybody know some medical statistics, or have some reliable and relevant information on this important aspect of weight training?