Implantation of automatic internal cardiac defibrillators (AICD) for management of arrhythmias necessitates the induction of ventricular fibrillation (VF) to test the device adequately. The profound hypotension associated with induced arrhythmia and subsequent circulatory arrest may result in cerebral ischemia. To characterize cerebral ischemia, we used a five-lead Lifescan brain activity monitor to examine changes in cerebral activity in 10 patients having AICD placement. The duration of hypotension, as defined by a mean arterial pressure (MAP) < 50 mm Hg, was recorded, and the corresponding changes in brain activity were evaluated during 51 episodes of circulatory arrest. The number of episodes for each patient ranged from 2 to 14. The average duration of hypotension per episode was 26.2 seconds, with a range of 8 to 67 seconds. Brain activity changes characteristic of cerebral ischemia occurred in 46 of the 51 events (90%). Cerebral ischemia did not occur when the duration of hypotension was less than 16 seconds (5 episodes). The duration of cerebral ischemia ranged from 50 to 279 seconds (average 84.9 seconds) and did not correlate with the duration of hypotension or the order of the episodes in the testing sequence. These findings suggest that reevaluation of standard monitoring practice for AICD implantation may be warranted.