The heart has an internal electrical system that controls the rhythm of the heartbeat. Problems can cause abnormal heart rhythms, called arrhythmias. There are many types of arrhythmia. During an arrhythmia, the heart can beat too fast, too slow, or it can stop beating. Sudden cardiac arrest occurs when the heart develops an arrhythmia that causes it to stop beating. This is different than a heart attack, where the heart usually continues to beat but blood flow to the heart is blocked.

There are many possible causes of cardiac arrest. They include coronary heart disease, heart attack, electrocution, drowning, or choking. There may not be a known cause to the cardiac arrest.

Without medical attention, the person will die within a few minutes. People are less likely to die if they have early cardiopulmonary resuscitation (CPR) and defibrillation. Defibrillation is delivering an electric shock to restore the heart rhythm to normal. 

Sudden Cardiac Arrest and Sudden Cardiac Death

(also called SCD and SCA)

Sudden cardiac death (SCD) is a sudden, unexpected death caused by loss of heart function (sudden cardiac arrest). SCD is the  largest cause of natural death in the United States, causing about 325,000 adult deaths in the United States each year.

SCD is responsible for half of all heart disease deaths. Sudden death occurs most frequently in adults in their mid-30s to mid-40s, and affects men twice as often as it does women. SCD is rare in children, affecting only 1 to 2 per 100,000 children each year
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How is a cardiac sudden death different from a heart attack?

Sudden cardiac arrest is not a heart attack (myocardial infarction). Heart attacks occur when there is a blockage in one or more of the coronary arteries, preventing the heart from receiving enough oxygen-rich blood. If the oxygen in the blood cannot reach the heart muscle, the heart becomes damaged.

In contrast, sudden cardiac arrest occurs when the electrical system to the heart malfunctions and suddenly becomes very irregular. The heart beats dangerously fast. The ventricles may flutter or quiver (ventricular fibrillation), and blood is not delivered to the body. In the first few minutes, the greatest concern is that blood flow to the brain will be reduced so drastically that a person will lose consciousness. Death follows unless emergency treatment is begun immediately.