Additionally, for patients in ventricular fibrillation, the proportion of patients discharged alive ranged from 14-30 percent in five cities where the outcome of EMS programs has been examined. These successes, however, concealed many failures in which CPR could not reverse death even though correctly applied within established periods between arrest and resuscitation. However, considerable potential existed for improving CPR techniques and for making additional inroads towards the estimated 100,000 deaths each year in the United States that could be reversed through the widespread application of CPR.