The cardiac dysfunctions traceable directly to pathologic changes in the thyroid may be grouped under three general headings: (1) those due to hypothyroidism; (2) those secondary to obstructed respiration, and (3) those occurring in hyperthyroidism. MYXEDEMA Zondek,1in 1918, first called attention to a type of cardiac disturbance occurring in hypothyroidism. In 1925, Fahr2reported four cases with dilatation of all the heart chambers, characteristic electrocardiographic changes and congestive failure, which did not respond to rest and digitalis but promptly yielded to thyroid medication. Reports of the cardiac status in myxedema have been made by Willius and Haines,3Thacher and White,4and Christian,5but not one of these investigators has reported any striking or constant manifestations of cardiac failure definitely traceable to hypothyroidism. Deviations from the normal electrocardiogram, such as inverted T wave (leads I and II) and low potential in all deflections, are not