Causes

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.

During times of low oxygen demand — when you're resting, for example — your heart muscle may still be able to function on the reduced amount of blood flow without triggering angina symptoms. But when you increase the demand for oxygen, such as when you exercise, angina can result.

• Stable angina. Stable angina is usually triggered by physical activity. When you climb stairs, exercise or walk, your heart demands more blood, but narrowed arteries slow down blood flow. 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. This can suddenly and severely decrease 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 isn't relieved by rest or your usual medications. If the blood flow doesn't improve, your heart is starved of oxygen and a heart attack occurs. Unstable angina is dangerous and requires emergency treatment.

• Prinzmetal's angina. This type of angina is caused by a sudden spasm in a coronary artery, which temporarily narrows the artery. This narrowing reduces blood flow to your heart, causing severe chest pain. Prinzmetal's angina most often occurs at rest, typically overnight. Attacks tend to occur in clusters. Emotional stress, smoking, medications that tighten blood vessels (such as some migraine drugs) and use of the illegal drug cocaine may trigger Prinzmetal's angina.