Gallop rhythm has long attracted the interest of both the clinician and the physiologist. It has always been regarded as a warning of a serious condition of the patient, and even though the belief that it invariably indicates a fatal issue has had to be abandoned, its grave prognostic significance is still unquestioned. The theories to explain the mechanism have been numerous, and consequently the literature on the subject is prolific. In this paper, we attempt to elucidate the dynamic factors connected with the production of this extra sound by means of graphic methods, giving exact records of the sounds and their relationship to the electrical and mechanical phenomena of the heart cycle. We are concerned only with the study of patients presenting the classic syndrome of Potain: gallop rhythm in cases of hypertension with more or less marked cardiac insufficiency. This type of patient is frequently found in hospitals,