The considerable number of publications regarding total thyroidectomy for the relief of cardiac disease have thus far largely been concerned with the basic physiologic reasoning which indicates the desirability of the procedure, the historical background which has steadily linked together thyroid function and cardiac action, the technic of the surgical operation and the clinical benefit to patients on whom the procedure has been carried out. With the clinical reports have appeared such laboratory data as can be utilized to measure either the changed cardiac function or the altered thyroid function.1 Coincident with these primarily clinical studies, there have appeared in fragmentary form a few articles dealing with the altered mechanism of the body apart from the changes commonly conceived as dependent on athyroidism and some physiologic experiments stimulated by the clinical studies. It seemed to us that a grouping of all the data which have been compiled in the