We report a case of circumflex artery stenosis after intraoperative radiofrequency ablation for permanent atrial fibrillation in a patient who had a previous mitral valve replacement. The patient presented with acute pulmonary edema and severe angina 1 year after an uneventful recovery. The patient underwent a diagnostic angiography that showed the presence of stenosis of a long segment of the circumflex artery, adjacent to the radiofrequency ablation site, which was reopened successfully by angioplasty. Intraoperative radiofrequency ablation caused circumflex artery stenosis. We believe that this complication could have been avoided by applying the radiofrequency ablation more distally between the left pulmonary veins and the mitral valve.