When someone collapses from sudden cardiac arrest, damage to the brain and vital organs begins in as little as four minutes if untreated.
Often the heart does not stop completely, but goes into ventricular fibrillation, in which the heart quivers rapidly but does not pump blood effectively. A shock from an AED can reverse this condition, restore the heart’s natural rhythm, and prevent permanent damage and death.
The shock from an AED is much more effective if it is delivered in the first few minutes after collapse. It is important to perform CPR until the arrival of a defibrillator for use.