Using an automated external defibrillator (AED) on a person who is having sudden cardiac arrest (SCA) can save the person's life.
The most common cause of SCA is an arrhythmia called ventricular fibrillation (v-fib). In v-fib, the ventricles (the heart's lower chambers) don't beat normally. Instead, they quiver very rapidly and irregularly.
Another arrhythmia that can lead to SCA is ventricular tachycardia. This is a fast, regular beating of the ventricles that may last for a few seconds or much longer.
In people who have either of these arrhythmias, an electric shock from an AED can restore the heart's normal rhythm (if done within minutes of the onset of SCA).