Cardiopulmonary resuscitation, or CPR, is a technique used to help keep oxygenated blood flowing until better medical help arrives, or until the heart recovers its normal rhythms. When cardiac arrest stops the heart from beating, CPR is indicated as an effective method of preventing brain damage. CPR is generally performed by placing the hands over the heart and pushing down up to one hundred times per minute, and optionally exhaling deep breaths into the lungs of the patient. These mechanical compressions of the heart allow its chambers to expel and refill with blood, keeping organs -- most importantly the brain -- from undergoing oxygen starvation and decay. While the assisted breathing has been shown to be helpful in certain conditions, it is not necessary for CPR to be effective.
It is important to know that cardiac arrest is not the same as a heart attack, although the conditions are similar: cardiac arrest is indicated by a lack of blood pumping to the heart, while a myocardial infarction (heart attack) is indicated when the heart muscle itself is starved of blood. Both conditions prevent the heart from pumping enough blood to the rest of the body, and symptoms can be similar; however, during a heart attack, the heart continues to attempt beating until it is exhausted from lack of blood, while during a cardiac arrest, the heart stops beating entirely.