TG and Graves disease: Mitral valve prolapse is a common finding, more frequently in Graves’ disease, secondary to endocardial myxomatous degeneration and glycosaminoglycan deposition, or loss of muscle tone with papillary muscle overdistention.17 Valvular insufficiency, in addition to the effects of thyroid hormone on pulmonary circulation, causes right ventricular failure more frequently than left ventricular failure in thyrotoxicosis.26 In a small percentage, dilation of all four chambers and reduced systolic function can be seen.44,45