HERE IS LITTLE DOUBT THAT SPEED in providing care represents the major determinant of survival for patients with out-ofhospital ventricular fibrillation (VF). That relationship has been documented for initiation of cardiopulmonary resuscitation (CPR) 1,2 as well as for the arrival of personnel and devices necessary for defibrillation. 3,4 Since 1970, the pattern for delivering out-of-hospital emergency care in Seattle, Wash, has incorporated rapidly responding first units staffed by emergency medical technicians (EMTs), followed as soon as possible by a later-arriving paramedic unit. 5 In 1980, we initiated the use of early defibrillation by EMTs in 4 firstresponding units. 6 Later, automated external defibrillators (AEDs) were extensively used. Whereas the survival experience of subsets of VF patients in Seattle seemed to be improved with AEDs, 7 the overall survival rate remained virtually unchanged (FIGURE 1) despite an approximately 3-to 4-minute shortened time to defibrillatory shock in most cases. Such a time saving had been predicted to increase survival by several percentage points. 3 Prompted by the lack of overall improvement in