Defibrillators are devices that restore a normal heartbeat by sending an electric pulse or shock to the heart. They are used to prevent or correct an arrhythmia, a heartbeat that is uneven or that is too slow or too fast. Defibrillators can also restore the heart’s beating if the heart suddenly stops. Types of defibrillator, placement of paddle, parts of automated external defibrillator (AED), steps in using AED, and caution are covered in this chapter. Types of defibrillator are manual external defibrillator, manual internal defibrillator, semiautomated internal defibrillator, automated external defibrillator, wearable cardiac defibrillator, monophasic waveform defibrillator, and biphasic waveform defibrillator.