it could be heartburn, gerd, or something to do with digestion. It could also be something to do with your irregular HB. I have had irregular HB been mistaken for gastro related through the years. I recently found out that it was A fib. The thing is that the two kind of go hand and hand. the heart and the esophogaus are very close to eachother and the pain assocaited with each can be similar.
Having said all that to say this. I would make sure that I didn't have something going on with my heart first. Then I would look at treating the gerd/reflux.
What kind of irregular HB do you have?
The best way to know if the burning sensation you are feeling is GERD: take Gaviscon and see if the pain dissolves.
Then you have your diagnoses and should keep a food diary and avoid the acid triggers.
The irregular heartbeat that you are referring to is most probably PAC's and PVC's. It is very common and not dangerous and does not need any medical intervention. If the Doctor found A-fib on your EKG, he would have mentioned it as it is a significant finding on an EKG.
All the best and let us know if the Gaviscon worked for you.