context: Cardiac arrest, which often leads to a heart attack, is frighteningly common: every minute of every day there is another victim, according to the American Red Cross. Almost 80% of cardiac arrests occur at home and are witnessed by a family member. Would you know what to do if someone you loved experienced a cardiac emergency? Make sure you're prepared -- take a CPR (cardiopulmonary resuscitation) class and get trained to use an automated external defibrillator, or AED. It could mean the difference between life and death. The automated external defibrillator is a computerized device used to restart a heart that has stopped beating, or is beating too quickly to create a pulse. Defibrillators work by shocking the heart back into action. Many public places, including airports, casinos, gyms, malls, and sporting venues, have defibrillators on hand in case of emergency. In the past, only trained medical professionals were able to use defibrillators. However, today's new automated external defibrillators can be used by anyone. The first step in saving a life is being able to recognize an emergency. Know the warning signs of a heart attack. Anyone who is unresponsive should receive emergency care. If you are with someone who complains of chest pain and then collapses, odds are he or she is having a heart attack or is in cardiac arrest. If possible, have someone else call 911 while you start CPR. CPR should be used when a person stops breathing and his heart has stopped beating. CPR keeps oxygenated blood flowing to the brain and heart until a defibrillator or emergency team arrives to get the heart beating normally. When started immediately following cardiac arrest, CPR can double or triple the victim's chance of survival. Here is how to do CPR for an unresponsive adult, child, or infant -- with the exception of newborns: Immediately call 911 and locate a defibrillator, if available. Don't be deterred if you don't know how to perform CPR: 911 operators are trained to walk people through the steps over the phone. After you have called 911, start CPR immediately. Remember CAB: C - Compressions: Place the heel of your hand on the center of the victim's chest. Put your other hand on top of the first with your fingers interlaced. Press down so you compress the chest at least 2 inches in adults and children and 1.5 inches in infants. One hundred times a minute or even a little faster is optimal. ( That's about the same rhythm as the beat of the Bee Gee's song " Stayin' Alive.") A - Airway: If you've been trained in CPR, you can now open the airway with a head-tilt and chin-lift maneuver. B - Breathing: Pinch the victim's nose closed. Take a normal breath, cover the victim's mouth with yours to create an airtight seal, and then give two, one-second breaths as you watch for the chest to rise. Continue compressions and breaths -- 30 compressions, two breaths -- until help arrives. Use an automated external defibrillator, if available. Attach it to the victim and use as soon as available. Followthe instructions supplied by the defibrillator. ( Most machines are programmed to talk you through the process, or a 911 operator can assist you.) Minimize interruptions in chest compressions before and after each shock. Resume CPR beginning with compressions immediately after each shock. CPR Tips: Chest compressions are extremely important. Even if you are not comfortable performing rescue breaths on a stranger, be sure to do chest compressions. It is normal to feel popping and snapping when you begin chest compressions. Try not to let your hands bounce when you are doing compressions. Let the chest fully recoil but keep your hands in place on the chest at all times. An automated external defibrillator, or AED, is very simple to operate. If you can press an "on" button, you can use an AED. Once the defibrillator is turned on, a computer-generated voice will walk you through the steps. Here is what to expect: You will be asked to place a set of adhesive electrode pads on the victim's bare chest and, if necessary, to plug the pads' connector into the defibrillator. The defibrillator will begin to automatically analyze the person's heart rhythm to determine if a shock is required. It is important that no contact be made with the person while the defibrillator is analyzing the heart rhythm. If the person is touched or disturbed, the test may not be accurate. If the defibrillator determines that a shock is necessary, it will automatically charge itself and tell you when to press the button that will deliver the shock. Once the shock is delivered, or if no shock is deemed necessary, you will be prompted to check to see if the person has had a return of normal breathing or circulation. If not, you will be reminded to start CPR. To become certified in CPR and in the use of automated external defibrillators, contact your local American Red Cross or American Heart Association to find a class in your area.