There is now both national and international acceptance of the "principle of early defibrillation," which contends that whoever arrives first at the scene of a cardiac arrest should have a defibrillator. The almost revolutionary technological event that permits widespread implementation of this principle has been the development of automated external defibrillators (AEDs). The simplicity, accuracy, and safety of these devices markedly expands the range of people who can deliver early defibrillation, which includes minimally trained emergency personnel, lay and community responders, and family members of high-risk patients. Even though AEDs now approach the status of "standard of care," the AED, as an example of a new technology, has not followed the classic technology paradigm: conceptualization, experimentation, dissemination, and standard of care. Instead, like many other technical innovations in emergency medicine, the development of AEDs proceeded simultaneously on many fronts, and implementation often occurred before confirmation of important subissues. AEDs may experience the life cycle of many new ideas: initial enthusiasm and widespread adoption, followed by disillusionment and rejection, and finally a mature, proper perspective. Careful implementation and continued evaluation may help emergency personnel avoid periods of disillusionment with AEDs and move steadily and uneventfully to a proper perspective.