CPR can be lifesaving, but it is best performed by those who have been trained in an accredited CPR course. The procedures described here are not a substitute for CPR training. The newest techniques emphasize compression over rescue breathing and airway, reversing long-standing practice. See www.americanheart.org for classes near you.
Time is very important when an unconscious person is not breathing. Permanent brain damage begins after only 4 minutes without oxygen, and death can occur as soon as 4 - 6 minutes later.
When someone starts CPR before emergency support arrives, the patient has a much greater chance of surviving. Yet, when most emergency workers arrive at a cardiac arrest, they usually find no one giving CPR.
Machines called automated external defibrillators (AEDs) can be found in many public places, and are available for home use. These machines have pads or paddles to place on the chest during a life-threatening emergency. They automatically check the heart rhythm and give a sudden shock if, and only if, that shock is needed to get the heart back into the right rhythm. When using an AED, follow the instructions exactly.