A man in his 40s with a 20-year history of bilateral sensorineural hearing loss was referred by his primary care physician for evaluation of left ventricular hypertrophy detected by echocardiography. The echocardiogram was performed because of an abnormal electrocardiogram demonstrating sinus tachycardia accompanied by high QRS voltage with a strain pattern in the precordial leads. He had no history of other illnesses. On physical examination, the patient was 154 cm tall and weighed 38 kg. The cardiovascular examination was unremarkable. Neurological examination showed mild cognitive impairment, poor coordination, and muscle weakness of the bilateral lower limbs. Blood test results revealed impaired glucose tolerance, hypothyroidism, and elevated levels of lactic acid (32.4 mg/dL) and pyruvate acid (1.91 mg/dL; to convert to micromoles per liter, multiply by 113.56). Review of the transthoracic echocardiogram showed diffuse hypertrophy, moderately decreased contractility of the left ventricle, and increased intramyocardial signal intensity (Video). The patient was admitted to the hospital for further evaluation. On admission, brain magnetic resonance imaging demonstrated cerebellar atrophy. Cardiac magnetic resonance imaging demonstrated diffuse biventricular hypertrophy and moderately impaired left ventricular systolic function. A wide range of nodular and band-shaped late gadolinium enhancement was detected in the middle and epicardial layers of the left ventricular myocardium. Coronary angiography revealed no significant stenoses of the epicardial coronary arteries.