Cardiomyopathy in Hyperthyroidism

To the Editor: The article by Forfar et al. in the November 4 issue¹ demonstrated a decrease in left ventricular ejection fraction during exercise in patients with hyperthyroidism. This reduction in function was contrasted with an increase in ejection fraction during exercise when the patients were euthyroid. Beta-adrenergic blocking doses of propranolol did not change the direction of these responses. The authors concluded that a reversible cardiomyopathy is present in hyperthyroidism. The concept of a cardiomyopathy in hyperthyroidism seems to contradict a number of well-known observations about thyrotoxicosis. First of all, the incidence of congestive failure is low in.