The following conclusions have been drawn from a study of 20 cases of total atrio-ventricular block, which were supra-His in 7 cases, intra-His in 4 cases, infra-His in 9 cases, and were with (11 cases) or without (8 cases) recent Stockes-Adams (1 case was excluded): resumption of the basal rhythm after the post-stimulatory pause is slower in cases of infra-His A-V block; automatic discharge from the focus is easily upset by rapid stimulation, whatever the site of the focus (ventricular or junctional); subsidiary foci of stimulation would behave from the electro-physiological standpoint like a sinus focus with reduced autonomy, and deprived of its peripheral zone of physiologically slow conduction; unfortunately electro-physiological investigation of this group does not allow us to separate with confidence those patients who have had Stockes-Adams attacks from those who have not.