Final answer:
An AED delivers a large shock to the heart to terminate ventricular tachycardia or fibrillation. It is designed to be used by laypersons and provides verbal instructions. CPR is recommended before using an AED.
Step-by-step explanation:
When a pulseless ventricular tachycardia (pVT) or ventricular fibrillation (VF) is detected, an automated external defibrillator (AED) is used to deliver a large shock of electrical energy to the person's heart. This shock terminates the arrhythmia and allows the body's natural pacemaker to resume its normal rhythm. AEDs are designed to be used by laypersons and automatically diagnose the patient's heart condition, apply the appropriate shock, and provide verbal instructions on how to use the device. CPR is recommended before using an AED in many cases.