A defibrillator is a medical device used to restore a normal heart rhythm in individuals experiencing life-threatening arrhythmias, such as ventricular fibrillation or pulseless ventricular tachycardia. It delivers an electric shock to the heart, which can help reset its electrical activity. Defibrillators come in various forms, including automated external defibrillators (AEDs) for public use and advanced devices used in hospitals. Quick access to a defibrillator can significantly improve the chances of survival in cardiac emergencies.