A defibrillator is a medical device used to restore a normal heart rhythm in cases of life-threatening arrhythmias, such as ventricular fibrillation or pulseless ventricular tachycardia. It delivers an electric shock to the heart, which can help reset the heart's electrical activity and potentially save a life. Defibrillators can be found in various settings, including hospitals, ambulances, and public places, and come in automated external defibrillator (AED) and manual versions.