Thanks for your Query at DoctorSpring.com,
Going through case history, these are the following possibilities,
!) Acid Peptic Disease
3) Due to heart
Since you have history of smoking I would suggest to do EKG and if abnormal to do echo cardiogram.
Mean while if your are having any proton pump inhibitors or antacids you can take it and see for relief , the probably you have Acid Peptic Disease.
In case you have any tenderness over the site you are complaining of pain, then probably it may be some muscular pain.
In case you are having pain the chest and gets aggravated by exertion or any simple activities and feel beeter with rest , then you may be dealing with heart and then you investigate further.