A defibrillator is a device that gives a high-energy electric shock to the heart of someone who is in cardiac arrest.
This high energy shock is called defibrillation, and it's an essential part of trying to save the life of someone who’s in cardiac arrest. A defibrillator may also be referred to as a Defib, an AED (Automated External Defibrillator), or a PAD (Public Access Defibrillator).