Thanks for your question on Health Care Magic. I can understand your concern. Since your extensive cardiac work up is normal, no need to worry for heart diseases for your pain. You are active smoker. And so you are at high risk of GERD (gastroesophageal reflux disease). Cigarette smoke actually causes laxity of gastroesophageal sphincter. So acid content of stomach tends to come up in the esophagus and cause burning central chest pain, belching, nausea etc. So get done upper GI (gastrointestinal) scopy for the diagnosis of GERD. If this is present than you need to start proton pump inhibitors. Quit smoking as soon as possible because it is not good habit. Hope I have solved your query. Wish you good health. Thanks.