A 14-year-old adolescent presented to our hospital with a complaint of syncope during exercise (playing basketball). He reported feelings of dizziness, sweating, and blackness before fainting. He denied having chest pain or abnormalities in limb movement before and after the occurrence of the episodes. He suffered from two similar episodes in the preceding 2 years while playing basketball and while running. He denied having a family history of coronary artery disease, cardiomyopathy, hypertension, and diabetes. He was diagnosed as experiencing a vagal syncope because of a positive tilt test result a year ago in a local hospital. However, a review of his previous medical records did not reveal any abnormalities. A physical examination on admission revealed normal levels of blood pressure (120/60 mmHg), heart rate (78 beats/min), respiratory rate (18/min), and oxygen saturation of 99% (room air). Cardiac and pulmonary examinations showed normal heart sounds without murmurs and with clear lungs. Laboratory test results indicated normal levels of blood glucose, high-sensitivity troponin, CK-MB, N-terminal B-type natriuretic peptide (NT-proBNP), D-dimer, CBC w/diff, and CMP. The renal and hepatic functions were within normal limits. The baseline ECG displayed sinus rhythm (HR = 78 bpm) without significant abnormalities (Figure 1A). Transthoracic echocardiography (TTE) showed normal cardiac structure and function (Figure 1B). To further investigate the possible reason for syncope, coronary CTA was performed, which revealed an anomalous origin of the LCA originating from the left side of the right sinus of Valsalva and ran between the aorta and the pulmonary artery with an intra-arterial wall course of approximately 20 mm in length (Figure 2A). To clarify whether the anomalous origin of the LCA was the real reason for syncope, we performed CT-FFR on all coronary branches at rest, which revealed an abnormal FFR of the left anterior descending artery (LAD, 0.79) but a roughly normal FFR of the left circumflex artery (LCX, 0.84) and the right coronary artery (RCA, 0.90) (Figure 2B). CT-FFR is a physiologic simulation technique that models coronary flow from routine coronary CTA. To evaluate lesion-specific ischemia, CT-FFR is measured 2 cm distal to a stenotic lesion. A CT-FFR value >0.8 is considered normal, values between 0.76 and 0.8 denote a borderline condition, and a value of 0.75 or less represents an abnormal condition. Since CT-FFR of the LAD was lower than normal at rest, we reasoned that it should be even lower during physical exercise. The cardiac team concluded that the AAOCA was the reason behind the patient's syncope, following which a surgical correction with a modified unroofing procedure was performed. One week after surgery, repeat CT-FFR was performed to evaluate the effectiveness of the corrective surgery, and the result showed a successful revascularization of the LCA (Figure 3A) and a significantly improved LAD flow with CT-FFR 0.91 (Figure 3B). CT-FFR of the LCX (0.91) and RCA (0.88) remained within normal limits. The patient was discharged 10 days after surgery and followed up on an outpatient basis. He soon resumed his normal activities and had no recurrence of syncope.