This restricts the flow of blood, and less oxygen reaches the heart muscle. This is by far the most common cause of angina. When the spasm stops, the artery and blood flow return to normal.
Abnormal heart valves.
Abnormal heart rhythms. An excess of red blood cells causes the blood to thicken. Some thyroid conditions. Angina is more likely to occur when increased demands are placed on the heart, as with exercise, emotional upset, exposure to cold air, and digestion of a big meal. However, angina may also occur at rest or even during sleep.