A medial illustration showing an acute coronary syndrome. The normal coronary artery may have asymptomatic atherosclerotic plaque (stable angina) that builds up inside the lumen. However, there are several coronary syndromes that can cause complications (artery occlusions) such as unstable angina, non-ST segment elevation myocardial infarction, and a ST-segment elevation myocardial infarction. An unstable angina is characterized by platelet aggregation and unstable plaque. The myocardial infarctions are characterized by a thrombus that blocks blood flow through the artery.