We report the case of a 42-year-old woman with aortic regurgitation discovered to be caused by a quadricuspid aortic valve (QAV) diagnosed by intraoperative transesophageal echocardiogram. With improvements in echocardiographic imaging, the diagnosis of QAV is likely to be made more reliably in the future and should prompt close clinical follow-up given the frequent association of this lesion with valvular insufficiency.