CPR extends the window of opportunity for professionals to perform more elaborate first aid procedures, but by itself it cannot save the majority of victims of sudden cardiac arrest. Most of the people who experience SCA have ventricular fibrillation (VF), which causes the heart muscle to quiver rapidly and beat improperly. CPR cannot correct VF. An electrical shock, known as defibrillation, is what's required to successfully restore a normal heartbeat in someone with the condition.
The shock itself doesn't switch the heart back on -- it's not like flipping a tripped circuit breaker. Instead, defibrillation actually stops the heart briefly. This gives the pacemaking cells a chance to re-establish a normal heartbeat.
So why do CPR at all if it can't address the root causes of sudden cardiac arrest? The bottom line is that CPR is an important part of a comprehensive response to a cardiac emergency. Defibrillation requires special equipment -- an automatic external defibrillator (AED) -- that has to be brought to the patient, and CPR can keep a patient alive until it arrives. In fact, defibrillation is less successful when CPR hasn't been performed [source: American College of Emergency Physicians].
CPR is helpful for those suffering from SCA, but does it pose any hazards to the person performing it? Check out the next section to learn more.