Angina is caused by reduced blood flow to your heart muscle. Your blood carries oxygen, which your heart muscle needs to survive. When your heart muscle isn't getting enough oxygen, it causes a condition called ischemia.

The most common cause of reduced blood flow to your heart muscle is coronary artery disease (CAD). Your heart (coronary) arteries can become narrowed by fatty deposits called plaques. This is called atherosclerosis.

This reduced blood flow is a supply problem — your heart is not getting enough oxygen-rich blood. You may wonder why you don't always have angina if your heart arteries are narrowed due to fatty buildup. This is because during times of low oxygen demand — when you're resting, for example — your heart muscle may be able to get by on the reduced amount of blood flow without triggering angina symptoms. But when you increase the demand for oxygen, such as when you exercise, this can cause angina.

  • Stable angina. Stable angina is usually triggered by physical exertion. When you climb stairs, exercise or walk, your heart demands more blood, but it's harder for the muscle to get enough blood when your arteries are narrowed. Besides physical activity, other factors such as emotional stress, cold temperatures, heavy meals and smoking also can narrow arteries and trigger angina.
  • Unstable angina. If fatty deposits (plaques) in a blood vessel rupture or a blood clot forms, it can quickly block or reduce flow through a narrowed artery, suddenly and severely decreasing blood flow to your heart muscle. Unstable angina can also be caused by blood clots that block or partially block your heart's blood vessels.

    Unstable angina worsens and is not relieved by rest or your usual medications. If the blood flow doesn't improve, heart muscle deprived of oxygen dies — a heart attack. Unstable angina is dangerous and requires emergency treatment.

  • Variant angina. Variant angina, also called Prinzmetal's angina, is caused by a spasm in a coronary artery in which the artery temporarily narrows. This narrowing reduces blood flow to your heart, causing chest pain.
Jul. 12, 2013