Thyrotoxicosis is an uncommon cause of low-output congestive heart failure. The case of a 41-year-old male who presented with severe symptomatic congestive heart failure, and was subsequently diagnosed with dilated cardiomyopathy secondary to hyperthyroidism, is presented. The cause of his hyperthyroidism was Graves disease. Despite an initial left ventricular systolic ejection fraction of 20% and evidence of global hypokinesis on echocardiography, treatment with antithyroid agents led to rapid improvement in his clinical status and normalization of his ejection fraction. The proposed mechanisms underlying the development of systolic dysfunction in thyrotoxicosis are discussed, and the literature on similar cases previously reported is reviewed.