This is most often due to Coronary Artery Disease. Sometimes, other types of heart disease or uncontrolled high blood pressure can cause angina.
In CAD, the coronary arteries, that carry oxygen-rich blood to the heart muscle, are narrowed, due to the buildup of the fatty deposits called plaque. This is known as artherscholorisis. Some plaque becomes hard and stable, leading to narrowed and hardened arteries. Other plaque is soft and likely to break open and cause blood clots.
The buildup of plaque on the inner walls of the arteries can cause angina in two ways. First, by narrowing the artery to the point where the flow of blood is greatly reduced… Second, by forming blood clots which are partially or totally block the artery.
Stable Angina is commonly caused by physical exertion. This leads to the pain and discomfort of stable angina. Severely narrowed arteries may allow enough blood to reach the heart when the demand for oxygen is low, such as when you are laying down. With exercise, like walking up a hill or climbing stairs, the heart works harder and needs more oxygen.
Unstable Angina is caused by blood clots that partially or totally block an artery. If plaque in an artery ruptures or breaks open, blood clots may form. This creates a larger blockage. The clot may grow large enough to completely block the artery and cause a heart attack. Blood clots may form, partly dissolve, and later form again. Chest pain can occur each time a clot blocks an artery.
Variant angina is caused by a spasm in a coronary artery. The spasm makes the walls of the artery tighten. This narrows the artery, causing the blood flow to the heart to slow or stop. Variant angina may occur in people with and without CAD.