Early on in death, the heart is fibrillating, not completely stopped. This is a good thing because it may be reversed with defibrillation, with CPR and emergency medications if defibrillation is ineffective. If the heart has stopped all activity, CPR and emergency medications can be given, but the likelihood of restarting the heart is a lot less.
If the person is just unconscious, opening the airway by NOT choking them any more, and positioning them so the airway stays open, is usually effective. Rescue breathing may be necessary, and supplemental oxygen may also be useful.
The consequences of depriving the brain of oxygen occur regardless of the cause, choking, heart attack, lightning strike, drowning - whatever. The longer the brain is deprived of oxygen the more likely there is to be permanent brain damage. The exact areas of the brain that are deprived of oxygen can affect the outcome, such as in an ischemic stroke where only one branch of an artery is blocked.
FWIW,
Clarissa