An anomalous aortic origin of a coronary artery is rare and surgical intervention is recommendedwhen the patient is symptomatic. We performed coronary artery bypassgraft surgery in a 21-year-old male patient with a right coronary artery anomalouslyoriginating from the left coronary sinus. The artery was significantly stenosed by externalcompression between the aorta and the pulmonary artery. However, the graftbecame occluded 1 year after the operation. In such cases, the dynamic nature of thestenosis can cause relatively intact antegrade competitive flow from the native coronaryartery and lead to an occlusion of the grafted artery. Methods for evaluating flowrates or intraluminal pressures of native arteries could be helpful in decision-makingin similar cases.