Defibrillators deliver a therapeutic dose of electrical energy to an affected heart. Defibrillators can be external or implanted depending on the type of device used or needed. Defibrillators can be found in hospitals and other patient care facilities as well as in ambulances and other emergency response vehicles as portable defibrillators. Some portable defibrillators, knows as automated external defibrillators (AEDs), automate the diagnosis of treatable rhythms themselves making it easier for untrained persons or people with little training to use. Home defibrillators are made to be easy to use, safe and reliable. Home defibrillators may be worthwhile for people at increased risk of cardiac arrest, especially those who live far from an emergency room. Home defibrillators are also useful in helping a heart attack survivor live through a second crisis.