A 61 year old woman who had been receiving treatment for ulcerative colitis for 14 years complained of respiratory discomfort on exertion and was diagnosed with severe mitral regurgitation due to mitral valve prolapse. Minimally invasive mitral valvuloplasty with right mini-thoracotomy was performed in our facility. Laboratory findings showed elevated levels of serum creatine kinase (CK) and CK-MB immediately after surgery. In addition to elevated levels of myocardial enzymes, ST depression was seen in an electrocardiogram on postoperative day 2 ; therefore, we suspected myocardial ischemia during the surgery. Despite the persistently elevated levels of myocardial enzymes, coronary angiography showed no significant abnormalities. Because of the possibility of false CK elevation, we performed CK electrophoresis, which revealed the presence of macro-CK type 1. CK-MB activity is often falsely elevated when determined by immune-inhibition in macro-CK patients, and that leads to the suspicion of myocardial ischemia. We considered that it may be highly difficult to identify macro-CK in a patient after cardiovascular surgery owing to elevated levels of myocardial enzymes in most such patients.