More than 200 years ago, Caleb Parry described cardiological manifestations of hyperthyroidism. Interaction of thyroid hormones and sympathoadrenal system (responsible for rhythm disorders) and direct effect of thyroid hormones on the cardiac muscle (responsible for occurrence of hypertrophy and cardiac insufficiency) have been recognized as the pathophysiological basis of cardiovascular disorders of patients with hyperthyroidism. The aim of the study was to retrospectively analyze surgically treated patients with different types of hyperthyreosis, and establish the incidence and clinical significance of the left ventricular dysfunction related to duration and treatment of hyperthyreosis. Evaluation of left ventricular function was based on the ejection fraction during exercise. Signs of hypertrophy were echocardiographically, radiographically and electrocardiographicaly recorded. Over the period 1993-1997 at the Surgical Department of the institute of Endocrinology in Belgrade 423 patients with hyperthyreosis were operated: 293 (69.26%) patients had Graves-Basedow's disease, 74 (17.49%) toxic adenoma, and 58 (13.28%) toxic polynodal struma. The average duration of the disease in patients with Graves-Basedow's hyperthyreosis was 5 yrs, and the average age of patients was 29 yrs; the average duration of hyperthyreosis in patients with toxic adenoma was 1.2 yrs, and in cases of toxic polynodal struma 17 yrs. Pathological response of ejection fraction during exercise was recorded in 60% of patients. Signs of hypertrophy of the left chamber were recorded in 17% of subjects, and insufficiency of the left chamber with congestive stasis in the lungs in 4.6% of patients. The most common ECG changes were: synus tachycardia, higher voltage of P and T waves, elevated amplitude of QRS complex, prolonged P-Q and shortened Q-T intervals. In 20% of cases atrial fibrillation was evidenced. One patient had ECG signs of myocardial infarction. Clinical features of left ventricular dysfunction in hyperthyroidism include: occurrence in younger patients with history of hyperthyroidism, progressive course and occurrence of congestive cardiac failure as well as reversible nature of all cardiac changes after radical therapy of hyperthyreosis which can be medical, surgical or irradiation.