Usually the blockages, or stenoses, develop slowly. There are two basic ways that this happens. In either case, the blood flow through the affected artery is reduced suddenly. New-onset angina is unstable when it occurs in patients who have never had anginal symptoms before. In patients who have had stable angina, the discomfort is more intense, more frequent, brought on by less effort, or different in character from the previously stable angina.
Unstable angina is a medical emergency.
About one of ten people with it go on to develop acute myocardial infarction. The adjective acute applies to situations that have just started and are at the most unstable stage. So, patients with unstable angina should be admitted promptly to the cardiology service in a hospital until it is clear whether or not their condition will progress to acute myocardial infarction.