Physical exercise does not prevent a first time heart attack since there are no clinical large studies verifying this, right?

Exercise and heart: I am not aware of any study which shows that exercise 'prevents' heart attacks. It does make one more likely to have a lesser heart attack in terms of post MI function. The physical and psychologic benefits may well 'prevent' some MI's but I don't know of any studies done to prove a statisfical difference in MI incidence between exercisers and nonexercisers.