If one or more of your coronary arteries becomes narrowed, the blood
supply to your heart muscle may be restricted. During exercise or emotional
stress your heart has to do more work than usual, and so the muscle needs
more oxygen. If the blood cannot deliver enough oxygen, the muscle will
“complain” by causing ANGINA. The commonest cause of narrowing of the coronary arteries is the
gradual build-up of fatty materials in their walls. This is
ATHEROSCLEROSIS. Angina happens when the build-up is enough to so
restrict blood supply, that the muscle does not receive enough blood-the
medical term for this is “ischaemia”. 
We do not know for sure what causes the fatty build-up, but we do
know some important “risk factors”. The main ones are:
smoking,
high blood pressure,
high blood cholesterol.
Your risk is also increased:
if you are overweight,
if you take little exercise,
if you have a history of angina and heart attack at a young age in a
member of your family.
But these risk factors do not make it certain that you will have heart trouble.
Some people develop angina without having any of these risk factors.
Rarely angina can also be caused if the muscle in the coronary arteries
contracts and goes into spasm. CORONARY ARTERY SPASM can usually
be treated with tablets.