A 63-year-old man was admitted with an acute anteroseptal myocardial infarction. Coronary angiography performed 3 hours after the onset of chest pain revealed 99% stenosis of the proximal left anterior descending coronary artery (LAD) with delayed filling and intraluminal thrombus distal to the stenosis. After the intracoronary injection of isosorbide dinitrate, the delayed filling disappeared and a subsequent intracoronary urokinase partially dissolved the thrombus. Repeat coronary angiography in the chronic phase disclosed 75% stenosis of the LAD and disappearance of the thrombus. Intracoronary acetylcholine provoked a coronary spasm at the stenotic site of the LAD, concomitantly with chest pain and ST-segment elevation in the anterior leads. The present case demonstrated that coronary spasm plays an important role in thrombus formation and acute myocardial infarction. To date, the concept has been postulated that a dynamic interaction between atherosclerosis, platelet aggregation and spasm may work to cause coronary thrombosis and subsequently lead to acute myocardial infarction. Our report shed light on the importance of coronary spasm in the pathogenesis of myocardial infarction.