BackgroundThe clinical features of mitochondrial cardiomyopathy (MCM) are diverse. It can present as hypertrophic cardiomyopathy or dilated cardiomyopathy. The diagnosis of MCM is challenging and usually based on biopsy.Case presentationThe 30-year-old man was admitted to hospital due to dyspnea for 1 month and edema of both lower extremities for 1 week. Echocardiography suggested a whole heart enlargement, a whole heart diminished function. Renal impairment and diabetes were observed. Coronary angiography showed single-vessel disease (90% stenosis in the ostium of a small marginal branch). Left ventricular endomyocardial biopsy was performed.ConclusionMyocardial histopathology demonstrated a large number of abnormal mitochondrial accumulation, so the diagnosis was considered as mitochondrial cardiomyopathy.