The large part of pathophysiology of cardiac arrhythmias has been clarified but still arrhythmias have bothered anesthesiologists. This study was done in order to investigate the incidence and nature of arrhythmias using Holter monitor for complete study during enflurane anesthesia. The patients were randomly allocated to two groups. Group I received succinylcholine 1.5 mg/kg, and Group II vecuronium 0.1 mg/kg, intravenously for intubation. Continuous electrocardiographic recordings on magnetic tape were made in 34 patients undergoing tympanoplasty during general anesthesia (thiopental(5 mg/kg)-muscle relaxants induction, and N2O(50%)-O2-enflurane(1.2%)-pancuronium maintenance). After completion of the recordings, the tapes were scanned to detect changes in rhythm using the analyzer. Complexes were further studied by readouts on standard ECG paper. The results were as follows: 1) The number of patients(n=14) who exhibited arrhythmias during anesthetic maintenance was significantly greater than that(n=4) during induction. 2) The incidence of occurrence of cardiac arrhythmias was 64.7%. There was no difference between two groups. If sinus tachycardia included, the incidence reached at 94.1%. 3) The frequency of supraventricular arrhythmias was more than two times that of ventricular ones. The arrhythmias occuning at the AV junction were the most common, and VPCs the second most common 4) There was no effect on the frequency in arrhythmia occurrence, of age, gender, preoperative ECG findings, intraoperative serum K(+), and intraoperative PaCO2 The discrepancy in the incidence of arrhythmia occurrence between complete and incomplete studies tells that great caution should be paid perioperatively, especially to the patients who have cardiovascular disorders.