Although excessive arteriovenous fistula blood flow may be a factor in the development of high-output cardiac failure, this diagnosis is easily over-looked. Surgical reduction of fistula blood flow can improve the condition. We here report a case of high-output cardiac failure due to excessive arterio-venous fistula blood flow in a hemodialysis patient. A 51-year-old man who had been treated with hemodialysis since 5 years ago was admitted for increasing cardiac failure. Echocardiographic evaluation of cardiac output and duplex measurement of the fistula confirmed the diagnosis of high-output cardiac failure due to excessive arteriovenous fistula blood flow. After surgical closure of the fistula, the signs and symptoms of cardiac failure subsequently subsided and both systolic and diastolic dimension of left ventricle much decreased.