shooin' with a handgun requires you to be vvvvery skilled at aim.
now imagine shooin' your heart.
you need to either hit the chambers (ventricles) or the aorta.
ifff you insist then try to figure out where your heart is as people may have slightly different anatomy. once you figure it out then you can shoot that heart
keep in mind that it will be the worst chest pain you will ever feel in your life and there is no backing out unless you are right next to a hospital, you will probably bleed out or become brain dead from low oxygen saturation