A 74-year-old man was hospitalized for intermittent third-degree atrioventricular (AV) block, sinus bradycardia, and syncope. He had a past history of myocardial infarction and congestive heart failure. Echocardiography revealed a left ventricular ejection fraction of 35%. An electrophysiologic study revealed inducible sustained monomorphic ventricular tachycardia with a cycle length of 240 ms. A transvenous Guidant Vitality T125 DR dualchamber cardioverter-defibrillator (ICD; Guidant, St. Paul, MN, USA) was implanted together with a Guidant 4087 atrial lead and a 0158 integrated bipolar right ventricular (RV) lead. The bipolar ventricular electrogram measured 6 mV, the pacing threshold was 0.9 V at 0.5 ms, and the pacing impedance was 752 ohms. Defibrillation testing was successful on two occasions with 21J shocks when ventricular fibrillation was sensed with a ventricular sensitivity programmed to the "least" value. All measured parameters at implantation were satisfactory. Ventricular sensitivity was then programmed at 0.27 mV (nominal value).Appropriate device function was established at a follow-up visit 15 days after implantation. The pacing threshold was 0.8 V at 0.5 ms and the ventricular electrogram measured 5 mV. A chest Xray demonstrated that the atrial lead was in the right atrial appendage and the right ventricular (RV) lead was displaced slightly away from the left diaphragm, consistent with displacement from the original position at the right ventricular apex. The patient refused further treatment.The patient was then lost to follow-up for 8 months. He returned complaining of recurrent near and frank syncope. Real-time recordings revealed crosstalk during atrial pacing with resultant ventricular inhibition and asystole when the AV delay was 180 ms (Fig. 1). ICD interrogation Address for reprints: Ali Mehdirad, M.D., Midwest Heart Rhythm,