A 73 year old man admitted to our hospital with pain and twitching on the pacemaker pocket. His past medical history included hypertension and right pneumonectomy due to lung cancer. The patient had a VDD pacemaker on the left side, which was implanted 9 years ago due to third degree atrioventricular block. The battery had replaced one year ago due to battery depletion. The cause after pacemaker replacement had uneventful. He felt twitching on the pacemaker pocket last night. The admission electrocardiogram revealed left bundle branch block, exaggerated pacemaker spikes in all leads with sinusal p wave (Fig. 1). His physical examination was unremarkable except rhythmic contraction of the left pectoralmuscle. There was no stimulation on another part of his body including diaphragm. The blood pressure was normal, 120/75 mm Hg. The chest radiogram was as shown in Fig. 2. We evaluated him with device interrogation. Electrical measurements revealed a ventricular lead amplitude of 5.0 V, sensitivity 2.80 mV and an impedance of 242Ω. The threshold of ventricular stimulation was 1.6 V at 0.40 ms. The generator of the pacemaker was unipolar. Besides the pacemaker was on VDD mode with ventricular bipolar lead while atrial parameters were stable. The cumulative ventricular pacing was 98%. We can say the ventricular lead impedance was decreased (a fall in lead impedance by more than 250Ω). While pulse amplitude is usually remained as 5.0 V at the time of the pacemaker implantation. In generally the pulse amplitude is decreased after threshold test for pacemaker longevity. In this case the pulseamplitudewas remained as 5.0 V. However the main problem was not the high pulse amplitude. We reduced the pulse amplitude to 3.0 V in order to reduce muscle stimulation. After that pectoral muscle stimulation finished instantly. However hewas suffering againwith twitching on pacemaker pocket in the same evening. The reasons of twitching on the pacemaker pockets were decreased impedance of ventricular lead and the unipolar polarity of the generator.We planned to replace of the ventricular lead. But he refused it because of the risks of complication and decreased lung capacity.