The probability of surviving a heart attack depends on the speed with which appropriate medical care is provided to the person experiencing the heart attack.  To decrease the response time to a patient suffering a heart attack, it has been recognized that those persons who are typically first to arrive at the scene of a medical emergency, including medical technicians (EMTs), firefighters, police and the public (hereinafter collectively referred to as "first responders") should be provided with portable, automated external defibrillators (AEDs).  A first responder equipped with an AED will have a greater likelihood of successfully treating the patient than those who arrive later at the scene.  An AED designed for first responder use would therefore improve the overall success rate of treating heart attack patients. 
Because the probability of surviving a heart attack depends on the speed with which appropriate medical care is provided to the patient, the American Heart Association (AHA) promotes the following "Chain of Survival" guidelines:
(1) Early access to emergency medical service (EMS), such as by activating an emergency response system;
(2) Early CPR initiated by a rescuer to help the patient survive until more advanced care arrives;
(3) Early defibrillation; and
(4) Early application of advanced cardiac life support (ACLS), such as airway management, drugs, etc. 
With the exception of item number 4, all of the above guidelines can be performed by a first responder with minimal or no training, if provided with sufficient instruction while at the scene. 
Even if the first responder does have some basic training in device operation and cardiopulmonary resuscitation (CPR), he or she may forget this basic training during the stress of reacting to a heart attack.  With wider deployment of AEDs in homes and public venues, the minimally trained or even untrained use of defibrillation devices will increase.  Although some devices already exist for providing CPR prompting and automatic defibrillation therapy, these devices rely on several hours of training experience and verbal cueing for the rescuer to follow.  In addition, visual prompting of CPR and defibrillation instructions is achieved only through readable text prompts.  Success is diminished due to having to rely on memory recall of CPR and other training protocols.  Even retraining and certification every two years is inadequate to ensure proper administration of CPR and defibrillation therapy. 
Consequently, a defibrillator is needed which is capable of successfully directing precise instructions to a first responder with minimal or no training through a cardiorespiratory event, i.e., CPR as well as AED device operation, by use of visual and aural instructions.  The defibrillator should be as simple and user friendly as possible so as to remove any impediment to use by a rescuer with minimal or no training.  Further, the defibrillator should be programmable so as to comply with any changes in the standard protocols for CPR and AED operation.