A 65-year-old woman with ovarian tumor was scheduled for abdominal total hysterectomy and bilateral adnexectomy under epidural anesthesia. Preoperative examinations revealed no abnormalities including ECG. Twenty minites after the epidural injection of mepivacaine, widened QRS complexes, which were diagnosed as complete left bundle branch block (CLBBB) later, appeared on ECG. At that time, heart rate (HR) was 150.min-1. CLBBB disappeared when HR decreased to 110.min-1 following the administration of pindolol and verapamil. The operation was postponed. Exercise-treated ECG showed neither CLBBB nor ischemic change even when HR increased to 160.min-1. Two weeks later the operation was attempted again. CLBBB appeared again twenty minites after the epidural injection of mepivacaine. The CLBBB disappeared 5 minites after the induction of general anesthesia when HR decreased to 100.min-1. The operation was performed uneventfully. The effective refractory period (ERP) is shortened with the increase in HR, but the shortning of ERP varies in different part of the cardiac conduction system. In tachycardia, ERP of left bundle branch is longer than that of right one. Because the cardiac conduction system is depressed by local anesthetics, it is speculated that ERP of left bundle branch is elongated further by mepivacaine and CLBBB appeared in this case.