We herein report the case of a 37-year-old woman in whom an anomalous origin of the left coronary artery from the pulmonary artery was surgically corrected. A magnetic resonance angiogram showed the left main coronary artery connecting to the right posterior portion of the pulmonary trunk, and exercise-stressed thallium-201 perfusion scintigrams demonstrated a large reversible anterior defect. She was successfully treated by direct aortic reimplantation of the abnormal left coronary artery. We were able to obtain a sufficient length of the left main trunk by excising the large cuff of pulmonary artery wall surrounding the ostium of the anomalous left coronary artery while transecting the pulmonary artery. Postoperative angiograms demonstrated a widely patent left coronary artery, a decrease in the size of the right coronary artery, and no collaterals, and exercise-stressed thallium-201 perfusion scintigrams demonstrated no remaining ischemic defect at all. Direct aortic reimplantation is an ideal operation but is still limited by the anatomical position of the left coronary artery. In this case, magnetic resonance angiography was an excellent method for deciding the optimum operative procedure for the anomalous left coronary artery. In addition, exercise thallium-201 scintigraphy was found to be useful in recognizing the revascularized effect of the left ventricle.