INTRODUCTION Tracings from clinical cases exhibiting auriculoventricular rhythm are comparatively rare, although the reports of Belski,1 Cowan, Fleming and Kennedy,2 and Hume3 suggest that the condition is not uncommon, at least as a transient manifestation, in certain more or less acute diseases that especially attack the heart, such as diphtheria, rheumatic fever and subacute endocarditis. It is undoubtedly rare in chronic cardiac disease, and is usually, but apparently not always, associated with extensive myocardial involvement. It may also be produced experimentally in normal persons by various disturbances of the inhibitory apparatus. Englemann4 was the first to recognize auriculoventricular rhythm, following his application of the first Stannius ligature in the frog. Lohmann5 obtained the rhythm in the mammalian heart. Since that time, a large amount of experimental work has been done, culminating in the studies of Meek and Eyster,6 who proved the actual auriculo-ventricular nodal origin of the rhythm by the