A 54-year-old female with pre-existing idiopathic moyamoya disease developed chest pain with acute myocardial infarction. Coronary angiography detected occluded and stenotic lesions in the coronary arteries. Right coronary artery stenosis was treated by balloon angioplasty and stenting. Because of the restenosis, on-pump cardiopulmonary bypass was performed. The operation was uneventful and no perioperative cerebral ischemic episode occurred. The conclusion is that on-pump cardiopulmonary bypass preserving intraoperative hemodynamic parameters at an optimal level is a safe procedure in a patient with moyamoya disease.