In this presentation the use of His bundle electrography in the diagnostic localization of atrioventricular conduction defects is discussed. The recording of the His potential allows an identification of conduction disturbances at a level above, in, or below the His bundle. Atrioventricular conduction can be stressed and latent conduction abnormalities thereby unmasked by atrial stimulation tests, such as the gradual increasing of the atrial driving rate, or the application of single atrial premature beats of which the coupling interval is gradually shortened. These stimulation methods make a quantitative characterization of the impulse conduction in the different parts of the A-V conduction system possible.