A 65-year old man with a diagnosis of aortic regurgitation from childhood referred to our hospital due to palpitations and dyspnea on exertion. Transthoracic echocardiography showed severe aortic regurgitation, but the form of left coronary aortic cusp was not detected clearly. Trans esophageal echocardiography revealed small left coronary aortic sinus covered with a rudimentary left coronary cusp. Right coronary angiography showed retrograde flow to left coronary artery, and pooling of contrast material in the aortic cusp. Cannulation into the left coronary ostium could not be performed, aortography revealed no antegrade left coronary blood flow. The patient underwent aortic valve replacement with mechanical valve after resection of the rudimentary left coronary cusp, and ascending aorta replacement using selective cerebral perfusion. The post operative course was uneventful. We report on a rare case of occlusion of left coronary ostium with a rudimentary aortic cusp.