Jan. 5, 2025 PLYMOUTH VOICE. An automated external defibrillator (AED) is a lightweight, portable device that delivers an electric shock through the chest to the heart when it detects an abnormal rhythm to bring the rhythm back to normal. They drastically improve the chance of surviving SCA- sudden cardiac arrest- when a sudden and unexpected loss of heart function stops the heart from beating normally. Having an AED immediately available is often the difference between life and death.