Acute myocardial infarction (AMI) caused by an occlusion of the left main trunk (LMT) is a rare angiographic finding. The prognosis is usually extremely poor, particularly in an elderly patient, unless complete reperfusion is rapidly established. We experienced a survival case of an elderly man with AMI at the LMT. A 91-year-old man with cardiogenic shock was referred to our hospital for the treatment of AMI. Left ventriculograms showed that akinesis in the anterolateral and apical wall segments had resulted in an ejection fraction of 30.8%. Coronary angiograms revealed a 90% narrowing at the ostium of the LMT. Intravascular ultrasound images showed a circumferential calcification at the site of the minimum lumen diameter of the LMT. We successfully dilated this calcified narrowing using a coronary stent, and the patient was discharged without complications 1 month later. The patient was asymptomatic 6 months later.