Although the technique of mouth-to-mouth resuscitation was used in biblical times, it was forgotten until the late 1950s, according to the University of Washington. In 1960, several doctors discovered that pressing on a person's chest could help circulate the blood in the body. The two techniques—mouth-to-mouth resuscitation and chest compression—were then combined as CPR. In 2008, the AHA revised its guidelines to include hands-only CPR. This version uses only chest compressions.

When a person goes into cardiac arrest, the heart stops beating, or stops beating effectively. This halts the flow of blood, according to the AHA. CPR helps a small amount of blood to continue to flow to the heart and brain until the emergency medical help arrives. When done correctly, CPR can double or even triple a person's chance of survival.

According to the AHA, you should yell for help right away and call 911 as you start chest compressions on an adult. Ideally, have someone else call 911 and get an AED while you begin CPR. If the victim is an adult who has been underwater, suffered trauma, or is intoxicated, begin CPR first, then call 911. Do CPR for about 2 minutes before calling. This is about 5 cycles of chest compressions and rescue breathing.

Start chest compressions, pressing hard and fast in the center of the victim's chest. The recommended chest compression rate is 100 to 120 per minute. If an AED is available, use it. Continue until the person revives or help arrives. Give rescue breaths if you are trained in conventional CPR (chest compressions plus mouth-to-mouth breaths) and you are confident in your ability to give this type of help. If you are confident, do cycles of 30 chest compressions then 2 rescue breaths. Otherwise, do chest compressions without stopping. You don't need to check for a pulse before beginning CPR.

Death can occur in minutes if a person having a cardiac arrest doesn't get treatment. CPR can help reverse cardiac arrest. If you know CPR and stay up to date with your training, you'll be able to help a person having a cardiac arrest.

The most common cause of sudden cardiac arrest is ventricular fibrillation (VF), according to the AHA. A heart in VF quivers and can't pump blood. A person in cardiac arrest needs CPR and a shock to the heart (defibrillation). An AED and other forms of defibrillation can sometimes stop the VF quivering and allow normal heart rhythm to resume.

The idea behind the AED was to enable non-medical people to help in the rescue of someone in VF cardiac arrest. An AED is about the size of a laptop computer. You attach the AED to the victim, and the device automatically analyzes the heart rhythm. If a shock is needed, the AED makes that decision and tells you to stand away from the victim so the shock can be automatically delivered. The AED gives verbal prompts to guide you through the resuscitation process.

If a person moves his or her arms or legs, the person most likely no longer needs CPR. Once emergency medical help arrives, they will take over the care of the victim.