['The purpose of the study is to investigate the influence of cardiopulmonary resuscitation (CPR) time before the first defibrillation.', 'The present study retrospectively analyzed the Utstein template records from April 1, 2002, to June 30, 2005. Patients who had out-of-hospital-witnessed cardiac arrest caused by cardiac disease and who presented with ventricular fibrillation (VF) as the initial cardiac rhythm were included in the study. Before April 1, 2003, the emergency medical technician (EMT) needed to obtain telephone permission before attempting defibrillation, and CPR was continued until permission was received (CPR first). On and after April 1, 2003, the EMT was immediately able to attempt a defibrillation without obtaining permission (shock first).', 'In 143 patients who had out-of-hospital-witnessed VF, 43 patients and 100 patients were treated with the CPR-first strategy and the shock-first strategy, respectively. The duration of CPR before the first defibrillation was longer in the CPR-first group than that in the shock-first group. The CPR-first group showed a higher rate of favorable neurologic outcome 30 days after (28% vs 14%; P = .048) and 1 year after cardiac arrest (26% vs 11%; P = .033) than those of the shock-first group. In the patients with witnessed VF, a stepwise multiple logistic regression analysis showed the CPR-first strategy to improve the neurologic outcome.'] Does shortening of cardiopulmonary resuscitation time before the defibrillation worsen the outcome in out-of-hospital VF patients?