The patient was a 47 year-old man, who has been known to have effort angina since September 1989. His exercise stress ECG has revealed ST elevation in V2-V4 with maximum exercise. He experienced severe chest pain lasting for an hour on the way to his office in the early morning on November 16, 1989, and was admitted to our hospital. His ECG and laboratory findings indicated typical acute anteroseptal myocardial infarction, but the coronary arteriography (CAG) which was performed 7 hours after the onset showed no significant stenotic lesion. After administrating nitrate and calcium antagonist, he has had no attack of angina pectoris and his exercise stress test has revealed no ST-T changes on his ECG. 1 month later, while antianginal drugs were discontinued in order to perform an ergonovine stress test, the patient frequently complained of left anterior chest pain with remarkable ST elevation in precordial leads on his ECG. The CAG at chronic stage revealed that there was a 99% stenosis at Segment 6 of the left anterior descending artery (LAD) which was supplied with good collateral flow from the right coronary artery. The LAD was completely occluded at Segment 6 after intracoronary administration of ergonovine maleate 0.005 mg to the left coronary artery. After the intracoronary infusion of isosorbide dinitrate, there was no significant stenosis seen in the LAD except the minimum wall irregularity at Segment 6. These findings suggested that coronary spasm might play a major role of the occurrence of acute myocardial infarction in this case.(ABSTRACT TRUNCATED AT 250 WORDS)