Anomalous origin of the left coronary artery from the main pulmonary trunk results in myocardial ischemia or infarction, and may be a cause of death in the first months of life. Some patients, however, develop satisfactory coronary collateral circulation and remain asymptomatic into adulthood. In these patients, myocardial perfusion and left ventricular function are not well understood. We report the case of a 17-yr-old female patient, suffering from anomalous origin of the left coronary artery from the main pulmonary trunk, who underwent reimplantation of the left coronary artery to the aorta. The preoperative permanent 201Tl defect of the left antero-lateral ventricular wall and the abnormal regional wall motion induced by stress exercise testing were fully reversed after the operation.