Angina (chest pain) can be stable or unstable.

• Stable angina occurs at predictable times with a specific amount of exertion or activity. It is relieved by rest and may continue without much change for years. Stable angina usually is relieved by rest within 1 to 5 minutes.
• Unstable angina may occur as:
  • A change in the usual pattern of stable angina.
  • Chest pain that occurs at rest or with less and less exertion, that may be more severe and last longer, or that is less responsive to nitroglycerin.
  • The onset of angina in a person who previously did not have it.
  Unstable angina means that blood flow has gotten worse because of increased narrowing or small blood clots that form in the coronary arteries. Unstable angina is a warning sign that a heart attack may soon occur, and immediate medical evaluation is required.

Signs of unstable angina

• Chest pain began within the past 2 months and has suddenly become more frequent or severe.
• New chest pain occurs 3 or more times per day.
• Chest pain develops after less and less exertion.
• Chest pain occurs at rest (with no obvious exertion or stress); it may awaken you from sleep.
• Chest pain is less responsive to nitroglycerin.