Moderation is the key.
Like a car, if you work the car hard the parts can wear out sooner.
However causes of heart attacks are many and can be complex.
An underlying undetected condition is very likely, possibly hereditary.
Could be many other causes and not necessarily due to lack of fitness or being over fit.
So fitness is definitely good for a healthy long life.
Moderate low impact excercise is one of the best things you can do for your body.
Staying on the middle path I call it 
