Unstable angina is chest pain that occurs at rest or with less and less exertion; the pain may become severe and last longer and it may not respond to nitroglycerin or rest.

Unstable angina is a change from stable angina—a pattern of predictable chest pain that is relieved by rest. Unstable angina is a warning sign that blood flow to the heart has become more impaired and that a heart attack may soon occur.

Unstable angina requires immediate medical evaluation.