My first wife died of a heart attack and she was only two weeks short of her 42nd. birthday. So it does happen to people in that age range.
Oh, how awful. Well... my cousin died at 43 of a heart attack, but they didn't call it "natural causes," they called it a heart attack. I guess it's a terminology issue, but geez. This is still just a shock. It's 12 hours since I heard it and I'm still kind of dazed.