Well, this is a maybe... CPR or Cardiopulmonary Resucitation, never came out as a means of reviving an injured or dysrhythmic (irregular heart beat) person, rather it was mean't to keep someone from going from death (When the heart stops beating and perfusing the body) to clinically dead (The brain has died therefore the person can't be brought back). The whole point of it is to simulate breathing using rescue breaths, to oxygenate the blood, and then use chest compression's to get that blood to the organ that really needs it; the brain. It's just mean't as a basic life prolonging means.
That doesn't mean that CPR never really brings back anybody. CPR normally doesn't bring anybody back, but some people have returned from it a process called spontaneous resuscitation, though this is rare. One method commonly used in tandem is the AED which can shock a heart into asystole (no heartbeat) therefore allowing it to reboot and begin beating again.