A defibrillator is a device that provides an electric shock to the heart to restore a normal heartbeat. It is used when the heart rhythm stops or becomes dangerously irregular, such as in the case of ventricular tachycardia or ventricular fibrillation. Defibrillation is the use of an electrical current to help the heart return to a normal rhythm when a potentially fatal arrhythmia is happening in the hearts lower chambers. Defibrillators can be found in hospitals, ambulances, and public places such as airports. There are different types of defibrillators, including external defibrillators, implantable cardioverter-defibrillators (ICDs), and subcutaneous implantable cardioverter-defibrillators (S-ICDs). Defibrillation can be a lifesaver for someone in cardiac arrest, and it is most effective when a healthcare provider delivers the shock as soon as possible after an arrhythmia starts.