A 23-year-old woman with an initial diagnosis of dilated cardiomyopathy for several years was referred to our center because of progressive congestive heart failure. Echocardiography showed a hypokinetic dilated left ventricle with globally impaired systolic function and an ejection fraction of 30%. We performed multislice cardiac computed tomography that revealed abnormal origin of the single coronary artery from the pulmonary trunk, lack of coronary arteries arising from the aorta, and abundant collateral flow from the bronchial artery to the anomalous coronary artery. This case report shows that cardiac computed tomography can be a valuable tool in the diagnosis of rare coronary anomalies.