Coronary artery fistulas (CAF) are a rare anomaly in which there is communication between a coronary artery and a cardiac chamber or another vascular structure. A giant congenital CAF to the left brachial vein was identified clearly by multidetector computed tomography (MDCT) in an 84-year-old woman who presented with orthopnea and continuous murmur. Electrocardiogram was almost normal, but chest X-ray showed marked cardiomegaly with pulmonary congestion. Transthoracic echocardiography showed that the wall motion of the left ventricle (LV) was normal, but with an abnormal cavity behind the LV. CAF was suspected and coronary angiography revealed that the CAF originated from the right coronary artery (RCA), connected to the giant vessel. However, because the drainage site was not clearly detected, MDCT was performed and it became clear that the CAF originated from the RCA. The left circumflex artery flowed into the giant vessel, and drained to the left brachial vein.