there is pain due to decreased blood and oxygen
supply to the heart. Once there's enough oxygen the heart tissue goes back to normal. There's stable (something you have been feeling for a long time in the same situation and hasn't changed) and unstable, the dangerous one, which can lead to myocardial infarction
(these two are called acute coronary syndrome
In myocardial infarction, the tissue actually dies, so even after the oxygen is restored, that particular part will never return to normal. Usually there's always a part that is only ischemic (low oxygen) but not dead yet, so its necessary to reperfuse (open those arteries) as soon as possible to save the sick but not dead tissue.
In a few words:
angina: reversible damage
infarction: irreversible, dead tissue.