To determine whether the association between mitral valve prolapse and Graves' disease is related to thyroid function, three groups of individuals were studied: 16 patients with Graves' disease and hyperthyroidism (hyperthyroid: T4 greater than 11.5 micrograms/100 ml), 16 patients with Graves' disease without hyperthyroidism (euthyroid: T4 less than 11.5 micrograms/100 ml), and 40 healthy individuals. The three groups were similar in age, sex distribution, and anthropometrical characteristics. 2. All patients were evaluated clinically and by M-mode and two-dimensional echocardiography to determine the presence of mitral valve prolapse. 3. The frequency of mitral valve prolapse was similar in the hyperthyroid (31%) and euthyroid patients (25%), but was higher than in the normal individuals (5%). The frequency of systolic murmur was higher in the hyperthyroid patients (75%) than the euthyroid patients (19%) or the normal subjects (0%); however, the presence of a murmur was not associated with mitral valve prolapse. Hyperthyroid (13%) and euthyroid (13%) patients had a higher frequency of clicks than the normal individuals (0%), and the presence of click was associated with mitral valve prolapse. 4. Although patients with Graves' disease have a higher frequency of mitral valve prolapse, this is not associated with thyroid function. The presence of a click but not the presence of a systolic murmur may be a clinical indicator of mitral valve prolapse in Graves' disease.
