From your description of your friend's symptoms he/she experienced Angina. Angina is a pain or discomfort in the chest or adjacent areas caused by insufficient blood flow to the heart muscle. This chest pain
is relieved by rest or medication within a short period of time (usually 15 minutes). The issue involved here is the myocardial oxygen
demand since your friend climbed the stairs.
Chest pain of a longer duration or pain appearing with a lower level of effort than before, even at rest, should be considered unstable angina
I advise that your friend should go to ER or to a doctor immediately so he/she can undergo cardiac specific tests such as 12 lead EKG, cardiac serum markers, stress test
, heart catheterization and even an echocardiogram
to determine the correct diagnosis.
American Heart Association suggest that a person needs to go to ER within 4 hrs after the onset of chest pain to save the heart muscle. Remember Time is Muscle!