A 65-year-old man was admitted to our hospital with acute myocardial infarction (MI). Emergency coronary angiography showed no significant organic lesions, but a myocardial bridge was found at the mid-left anterior descending artery An acetylcholine provocation test revealed 90% spastic stenosis just proximal to the myocardial bridge. His acute MI could have been caused by both a coronary spasm and the myocardial bridge.