For what length of time can a heart attack last before it kills you?

Not very long: A heart attack can kill within minutes, actually. That's why it is so important to get treated right away if someone has a heart attack.

It may not!: Some damage is not lethal at all! depends on atherosclerosis, degree of obstruction, part of heart involved, and one's other life risk factors. Smoking obesity prior damage poor conditioning sedentary.