Although both Angina and Heart Attack indicate the same basic defect, i.e. reduced blood supply to the heart, there are differences.
The heart needs more blood when it has to do more work. With narrowed blood when as in Angina, there is a situation of temporarily reduced blood supply, which leads to chest discomfort and pain. Angina is precipitated after exertion, as the demand exceeds supply which leads to pain. But, there is no permanent damage to the heart muscle and the pain is reduced after rest. This is called Stable Angina.
But, sometimes Stable Angina (angina where the symptoms are relieved by rest or medicine) is converted to Unstable Angina.