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Tachycardia-induced cardiomyopathy secondary to thyrotoxicosis: a young man with previously unrecognized Graves' disease.

A young man with previously unrecognized Graves' disease presented with atrial fibrillation and severe low-output heart failure due to dilated cardiomyopathy. The patient's cardiomyopathy resolved and cardiac function recovered shortly after hyperthyroidism and tachycardia were treated during hospitalization. The temporal relationship between heart rate and cardiac function during the recovery period suggests that chronic tachycardia may have been an important cause of his cardiac dysfunction. Thyrotoxicosis seemed to be directly responsible for the development of sustained supraventricular tachycardia in this patient, which then led to tachycardia-induced cardiomyopathy causing severe low-output heart failure. Although relatively infrequent, this etiology should not be overlooked in patients thyrotoxicosis and heart failure. This is the first case in which the time course and the temporal relationship between the control of heart rate and the recovery of cardiac function are illustrated in a thyrotoxic patient.