Stop doing whatever it is that causes your symptoms, remain calm, and call nearest hospital. Immediate help and intervention is your best chance for survival if you are having a heart attack or other serious problem.
Lie down in a comfortable position with your head up.
If you have regular adult aspirin or its equivalent, chew one (as long as you are not allergic to aspirin). Chewing more than one will not do any good and may cause unwanted side effects.
If you have had angina before and been evaluated by your health care provider, follow his or her recommendations.
This may mean rest, and the immediate use of sublingual nitroglycerin.
It may include a visit to the hospital emergency room.