Using His bundle recordings and ventricular stimulation retrograde conduction was studied in 57 cases of complete AV block. VA conduction was observed in 13 patients. Of the 13, 12 had AV block distal to H, and during cardiac pacing 5 of them showed a retrograde His bundle potential. In all cases the AV node-His pathway was implicated in the transmission of the retrograde impulse. There was no retrograde atrial response in the remaining patients. VA block usually occurred at the same level as AV block. Nevertheless, two cases of AV block distal to H were associated with concealed retrograde conduction which stopped within the AV node.