Intra-His and infra-His block

52 cases of intra-His and/or infra-His block （including intraventricular block 25 cases） demonstrated by His bundle recording were reported. 29 of these patients had history of syncopy attack and 6 of them syncope was prevented after pacemaker implantation.In all 22 patients with intra-His or infra-His delayed conduction but no intraventricular con- duction defect, P-R prolongation due to H and/or HV interval lengthening displayed only in one patient. Therefore, it meant that majority of intra and/or infra-His conduction delay was concealed in conventional EGG recording al though 54％（12/22） of them sustained syncope episodes. The cases with intraventricular conduction defects can be divided into three and subdivided into seven categories according to electrophysiologic study, and in such a way more precise location of conduction impairment would be ascertained. 25 cases of intraventricular block presented syncope and 11 of them, the HV interval was more than 70ms. 5 of these symptomatic patients had pacemaker implanted with good result. 2 patients with LBBB developed sudden complete AV block during the procedure of His bundle recording. We suggest a standby pacing electrode in right ventricle when right catheterizationis contemplated in I, BBB patient especially with history of previous syncope attack.Whenever recurrent syncope cannot properly explained with extracardiac causes, electrophysiologic study is necessary even the conventional EGG fail to show any conduction defect.