So death from a heart attack is due to loss of blood...
I didn't think so, it is from the brain being deprived of O2.
A broadhead, bullet, electrical shock or a thousand other reasons can cause the heart to not beat.
A bullet obliterating the heart muscle will cause some blood loss, but not the 15% or more of your total supply needed to kill you.
While you will bleed out over time, you will be unconscious almost instantly because the brain can't work without a fresh supply of oxygenated blood.
Now you can cut off your arm and you will most likely remain conscious for a significant amount of time...at least compared to the victim without a beating heart ie: blood pressure.