Sudden cardiac arrest is when the heart's lower chambers (ventricles) suddenly develop a rapid, irregular rhythm (ventricular fibrillation) and the quivering ventricles cannot pump blood to the body. Within seconds, the person will not have a pulse and will be unconscious. Without immediate treatment, the condition is usually fatal.

Sudden cardiac arrest is not a heart attack, which is a problem with the plumbing of the heart; when blockage of one or more coronary arteries results in heart muscle damage. .

There are no prior symptoms of sudden cardiac arrest. However, these risk factors have been identified as increasing the risk of sudden cardiac arrest.

Treatment begins with cardiopulmonary resuscitation (CPR) {emergency measures to keep the blood flowing to the vital organs of the body}. An external defibrillator is needed to reset the heart rhythm. After the heart is in a normal rhythm, medications and an implantable defibrillator are usually prescribed.