Automated External Defibrillators (Semi-Automatic or Fully Automatic) are computerized, handy and practical devices that can help prevent death due to SCA (sudden cardiac arrest). These devices can monitor the rhythm of the heart finding out ventricular fibrillation (VF) or ventricular tachycardia (VT) and, if needed, are able to deliver an electrical shock to the heart to restore its regular rhythm.AEDs work exactly like a traditional defibrillator in a hospital and are now increasingly available in public places to allow almost anybody to treat SCA.Never think that AEDs can substitute the CPR (cardiopulmonary resuscitation) sequences. All people trained to operate an AED has surely been trained in CPR. In fact early CPR is a critical step in resuscitation to help restore the blood circulation and deliver oxygen to the body.In this case AEDs guide the rescuer for the correct CPR sequences while carry on analyzing the patient’s heart rhythm.At the same time, CPR cannot substitute the AED. Even if CPR is given, studies have shown that survival decreases 7-10% for each minute of waiting time before defibrillation is carried out.