Rate-dependent left bundle branch block during general anesthesia is rare, but its occurrence makes the electrocardiographic diagnosis of acute myocardial ischemia or infarction difficult. It can also be confused with slow rate ventricular tachycardia. Herein, a case of rate-dependent left bundle branch block, in a patient with no previous history of ischemic heart disease, is reported. The administration of esmolol resulted in a decrease in the heart rate, with reversion to normal sinus rhythm.