It can happen in a heartbeat or rather the absence of one. For whatever reason, the heart stops heart attack, electrocution, drowning, etc. When the heart stops, the blood stops flowing; the heart and brain no longer receive blood and tissue begins to die. In four minutes, there is damage; in seven minutes, there is irreversible damage.
That's why Cardio Pulmonary Resuscitation saves lives. It doesn't restart the heart; it just keeps the blood flowing to vital organs until more sophisticated aid such as electric shock paddles or injectible drugs arrive on the scene. Once CPR is begun, it is continued until the heart starts beating or the patient is declared dead.
The practice of CPR is as old as the Bible. A passage in the Book of Kings describes the Hebrew prophet Elisha warming a dead boy's body and placing his mouth over his. And from there came a long progression of techniques designed to return heartbeat and respiration to an unconscious person. Earlier methods had the victim lying prone with the arms extended overhead while the aid person alternately pressed forward on the back and pulled back on the arms.
In the 1960's came CPR with the victim lying on his back. The aid giver was supposed to Clear the airway and Check for pulse. If two people were administering CPR, one could do the chest compressions and the other could do the respiration. If just one aid giver was present, he/she had to alternate compressions with breaths, a ratio of 30:2 an exhausting process if it went on for very long. The problem was that a lot of people were not able to detect a pulse even when it was present. Another problem, which has increased over the years, was fear of infection in doing mouth to mouth respiration. Still, this method saved countless lives.
Except for cold-water drownings in which the window of life is extended, the first seven minutes after cardiac arrest are vital. When CPR is performed, enough blood is circulated to keep vital brain and heart tissues alive. Recently, it has been recommended that compressions alone are enough except in cases like drowning. In fact, it has been found that victims often do just as well or better with just the compression. Aid givers are more willing to give chest compressions than mouth to mouth respiration. Experiments have been done with abdominal compressions as well which may prove to better at retaining circulation than chest compressions. An additional benefit of abdominal compressions is that there is no risk of breaking ribs.
There are conflicting ideas about giving self CPR in the case of a suspected heart attack. One publicized idea is that of coughing deeply. A person in the midst of a heart attack might strain the heart further with such a maneuver. Another suggests draping oneself over a chair so that the pressure of the chair compresses the chest. If a person is truly in need of CPR, he or she will probably be unconscious. Better to use those last few seconds of consciousness to call 911.
We've seen CPR administered from the earliest history of human life. It's a frequent story in our news when someone comes to the aid of another whether it is a human or animal with the life-sustaining hands on first aid that keeps our blood flowing.
One final note. Television portrays CPR as being highly effective. On television, 75% of victims are saved. In real life, survival from cardiac arrest victims who receive CPR is only 22% to 41%. But that shouldn't discourage anyone from trying. A 22% chance at life is better than no chance at all.