Casino security officers used an automatic external defibrillator in 105 patients whose initial cardiac rhythm was ventricular fibrillation . 53% of the patients survived to discharge from the hospital. Among the 90 patients whose collapse was witnessed, the time interval to the delivery of the first defibrillation shock was 4.4±2.9 minutes. The survival rate was 74% for those who received their first defibrillation no later than three minutes after a witnessed collapse and 49% for those who received their defibrillation after more than 3 minutes. The mean interval to the arrival of paramedics was 9.8±4.3 minutes.