[Functional status of the myocardium in thyrotoxicosis]

Twenty-two patients with thyrotoxicosis, showing no clinical signs of heart failure were examined electro- and echocardiographically. Bicycle ergometry was also used in 13 of those. Central and intracardiac hemodynamics were assessed at rest, as was cardiovascular response to exercise. The results were compared to similar parameters in 18 normal subjects. Echocardiography demonstrated hyperkinetic circulation and normal myocardial contractility in the resting patients. Bicycle ergometry showed considerably limited working capacity in those patients. Limited chronotropic and inotropic reserve of the heart in the presence of increased left-ventricular operation at rest may be pathogenetically involved in reduced stress tolerance, seen in patients with thyrotoxicosis.