80 patients, 40 patients without preexisting EKG abnormality (group 1) and 40 patients with preexisting abnormalities of EKG (group 2), receiving general anesthesia in the operating room were monitored continously with electrocardioscope, Servomed SMK 155-1 and were recorded. 1) 7 cases(17.5%) of group 1 developed a variety of arrhythmia, and 13 cases (32.5%) of group (32.5%) of group 2 developed a variety of arrhythmia. 2) The most common arrhythmia was premature ventricular contraction including bigeminies (13 cases, 60% of the total arrhythemia) and the most serious arrhythmia was seen 1 case of rapid ventricular tachycardia without artrial activity. 3) Continous cardiac monitoring is valuable, easy and practical in virtually all instance during anesthesia and surgery.