There is a mysterious condition called 'Syndrome X' whose victims feel chest pain that may, perhaps, possibly, be related to a very slight constriction of the tiniest little arteries of the heart, but the cause of the pain is not understood at all. It is thought to be related to a highly sensitive nervous system, and it is much more common in women than men.
One thing necessary to diagnose it is a treadmill test showing that the patient's heart is in fact not quite getting enough oxygen--although it's important to understand that people with Syndrome X are usually NOT in danger of real cardiac problems. Have you had a treadmill test recently, and if so, how did you do?
More info here:
And on google, generally.
It couldn't hurt to post your question on the heart expert forum here: