A 52-year-old man with inflammatory disease of unknown origin but no specific laboratory abnormalities was referred to our hospital. He has subsequently diagnosed as having adult Still's disease. During an episode of severe inflammation he suffered reversible myocardial damage as revealed by electrocardiography, echocardiography and 201Tl myocardial scintigraphy; this was ameliorated by treatment with steroids and immunosuppressive drugs. No significant stenosis of the coronary artery was observed on coronary angiography. Interstitial mononuclear infiltration was apparent in the right ventricle on endomyocardial biopsy. Myocardial injury with adult Still's disease, which may result in heart failure, has rarely been reported. We report a case of adult Still's disease with myocardial dysfunction that may have been caused by microangiopathy.