Thanks for posting your query.
Normal EKG with chest x ray
does not mean that you do not have cardiac ailments.
Are you getting chest dullness during resting state or during exertion?
Sometimes cardiac diseases are precipitated during exertion.
You should consult with physician and go for endoscopy
Any type of ischemic cardiac disease are picked up by TMT as hear has 3 arteries and any type of block may cause changes in heart tracing during TMT.
If TMT is found to be abnormal then you have to go for 2 D Echo and coronary angiography
Endoscopy for detail analysis of UGI tract. Peptic ulcer disease
with GERD may cause your described symptoms.
If Endoscopy and TMT is normal then you may have panic attacks and you should consult with psychiatrist
Get well soon,
Dr. Mayank Bhargava