A 10-month-old boy was referred for tachypnea and heart murmur. An echocardiogram showed unexplained left heart dilation without evidence of an intracardiac shunt. A 64-slice computed tomographic contrast-enhanced angiography showed a large tortuous anomalous artery arising from the descending thoracic aorta and supplying the lower lobe of the left lung. The venous return into the left atrium was normal. The affected lobe had normal lung parenchyma, and its bronchial tree was connected normally with the left main bronchus. Hence, it was not a sequestrated lobe. The boy underwent surgical lobectomy of the left lower lobe and improved. Anomalous arterial supply of a lobe without sequestration of its bronchial tree is a rare pathologic entity. It also is a very rare cause of congestive heart failure in children. Computed tomographic angiography was a useful tool for evaluation of the intrathoracic anomalous vessel in this case.