Background: A 35-year-old man with primary antiphospholipid syndrome and no risk factors for atherosclerosis presented with postinfarction angina. Investigations: Coronary angiography, intravascular ultrasonography, injection of apolipoprotein-E-knockout mice with patient's IgG. Diagnosis: Myocardial infarction caused by a newly occluded proximal left circumflex artery. The left anterior descending artery exhibited a recanalized thrombus throughout the vessel. Management: The patient was managed by intensive angicoagulation including aspirin, clopidogrel, and enoxaparin for 2 months. After follow-up coronary angiography, he was switched to warfarin with a target International Normalized Ratio of 3.5-4.0.