An 88-year-old male patient arrived at our emergency department with a 3-hour history of acute crushing retrosternal chest pain. The chest pain began while he was asleep. He had no history of spontaneous bleeding, smoking, hyperlipidemia, diabetes mellitus, atrial fibrillation, or family history of coronary artery disease. However, he had hypertension and underwent tracheotomy because of laryngocarcinoma 7 years previously. The physical examination showed that his respiratory rate was 22/min, heart rate was 46/min, and blood pressure was 110/70 mmHg. His neck veins were not distended, and his breath sounds were clear. His heart rhythm was regular and heart sounds were clear with no murmurs. Peripheral pulses were intact with no edema. His initial electrocardiogram (ECG) showed ST-segment elevation in the inferior (II, III, and aVF) and anterior (V3–V6) leads, which was considered to indicate acute inferior and anterior myocardial infarction. However, his second ECG in the cardiac care unit had changed to show ST-segment elevation in the inferior leads but ST-segment depression in the anterior leads. The patient underwent primary angioplasty after receiving aspirin (100 mg) and clopidogrel (300 mg). Coronary angiography revealed that the right coronary artery (RCA) was acutely and totally occluded at the midportion and that the proximal and midportion of the left anterior descending coronary artery (LAD) had a hazy filling defect, which suggested an acute thrombus. We inferred that the RCA and LAD had first totally occluded simultaneously, followed by spontaneous partial lysis of the LAD thrombus. Intervention of the RCA was performed first, and only because of TIMI III flow in the LAD was glycoprotein IIB-IIIA inhibitor subsequently injected into the LAD. The patient’s symptoms and postoperative ECG results were significantly improved. After the operation, the patient received antiplatelet and antithrombotic therapy, aspirin, clopidogrel, low-molecular-weight heparin, and glycoprotein IIB-IIIA inhibitor. ECG after the procedure showed an ejection fraction of 54% with mild hypokinesia of the inferior walls. Creatine kinase-MB fraction levels peaked 12 hours later at 310 ng/mL (normal, 0–4.3 ng/mL). After the procedure, the patient had an uneventful course with no evidence of pulmonary congestion or recurrence of chest pain. The patient was discharged home 10 days later on aspirin, clopidogrel, a statin, a beta blocker, and an angiotensin converting enzyme inhibitor.