What causes Angina ? 

Underlying Causes
                
Angina usually is a symptom of coronary heart disease (CHD). This means that the underlying causes of angina generally are the same as the underlying causes of CHD.
                
Research suggests that CHD starts when certain factors damage the inner layers of the coronary arteries. These factors include:
                
Smoking
                
High amounts of certain fats and cholesterol in the blood
                
High blood pressure
                
High amounts of sugar in the blood due to insulin resistance or diabetes
                
Plaque may begin to build up where the arteries are damaged. When plaque builds up in the arteries, the condition is called atherosclerosis (ath-er-o-skler-O-sis).
                
Plaque narrows or blocks the arteries, reducing blood flow to the heart muscle. Some plaque is hard and stable and causes the arteries to become narrow and stiff. This can greatly reduce blood flow to the heart and cause angina.
                
Other plaque is soft and more likely to rupture (break open) and cause blood clots. Blood clots can partially or totally block the coronary arteries and cause angina or a heart attack.
                
Immediate Causes
                
Many factors can trigger angina pain, depending on the type of angina you have.
                
Stable Angina
                
Physical exertion is the most common trigger 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're sitting.
                
However, with physical exertionlike walking up a hill or climbing stairsthe heart works harder and needs more oxygen.
                
Other triggers of stable angina include:
                
Emotional stress
                
Exposure to very hot or cold temperatures
                
Heavy meals
                
Smoking
                
Unstable Angina
                
Blood clots that partially or totally block an artery cause unstable angina.
                
If plaque in an artery ruptures, blood clots may form. This creates a blockage. A clot may grow large enough to completely block the artery and cause a heart attack. For more information, go to the animation in "What Causes a Heart Attack?"
                
Blood clots may form, partially dissolve, and later form again. Angina can occur each time a clot blocks an artery.
                
Variant Angina
                
A spasm in a coronary artery causes variant angina. The spasm causes the walls of the artery to tighten and narrow. Blood flow to the heart slows or stops. Variant angina can occur in people who have CHD and in those who dont.
                
The coronary arteries can spasm as a result of:
                
Exposure to cold
                
Emotional stress
                
Medicines that tighten or narrow blood vessels
                
Smoking
                
Cocaine use
                
Microvascular Angina
                
This type of angina may be a symptom of coronary microvascular disease (MVD). Coronary MVD is heart disease that affects the hearts smallest coronary arteries.
                
Reduced blood flow in the small coronary arteries may cause microvascular angina. Plaque in the arteries, artery spasms, or damaged or diseased artery walls can reduce blood flow through the small coronary arteries.