Figure-1：AAI pacing mode and frequent premature ventricular contraction(PVC). ①Judging from QRS morphology of the PVC: it originated from the scar zone of old myocardial infarction in the posterior inferior left ventricle.②AP+VSP overlapped in PVC?③AP overlapped in PVC when VSP function turned off. EGM 1:Atip to Aring;EGM 2:Can to RV coil;EGM 3: RVtip to RVring (AP: atrial pace; PVC: premature ventricular contraction; VSP: ventricular safe pace; VP:ventricular pace)