Sudden cardiac arrest (patient information)
Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Sudden cardiac arrest (SCA), also known as sudden cardiac death, is when the heart suddenly and unexpectedly stops beating. When this occurs, blood stops flowing to the brain and other vital organs. SCA usually causes death if not treated in minutes.
The heart has an internal electrical system that controls the rhythm of the heartbeat. Problems with the electrical system can cause abnormal heart rhythms, called arrhythmias (ah-RITH-me-ahs). There are many types of arrhythmia. During an arrhythmia, the heart can beat too fast, too slow, or it can stop beating. SCA occurs when the heart develops an arrhythmia that causes it to stop beating.
SCA is not the same thing as a heart attack. A heart attack is a problem with blocked blood flow to a part of the heart muscle. In a heart attack, the heart usually does not suddenly stop beating. SCA, however, may happen during recovery from a heart attack.
People with heart disease have a higher chance of having SCA. But most SCAs happen in people who appear healthy and have no known heart disease or other risk factors for SCA. Outlook
Ninety-five percent of people who have SCA die from it, most within minutes. Rapid treatment of SCA with a device that sends an electrical shock to the heart (called a defibrillator) can be lifesaving. Automated external defibrillators (AEDs), which are often found in public places like airports and office buildings, can be used to save the lives of people having SCAs.