Sounds like some kind of arrhythmia. This is quite common in a lot of people and it can occur in perfectly healthy people. You've done the right thing to get it checked out, though. Arrhythmias can be caused by lifestyle issues or health problems and its recommended that you focus on lifestyle first as well as seeing a doctor to check your general health. The "burning" you talk about may be heartburn, and therefore stomach related, which can have an effect on your heart-rate.
At this point I'd like to address Admin regarding lifestyle issues. Basic guidelines regarding diet and daily routine and tips to prevent/reduce benign arrhythmias would be useful as a sticky on this site. It would be very useful for people like Heather who have just started having noticeable symptoms.
I posted how my lifestyle changes made a big difference to my symptoms. While every case is different, most of us have hectic lives that stop us taking proper care of ourselves. This is true for my case. Do a search for my username on this site or check the links below.
Please take a look at issues covering lifestyle/diet Here:
Good luck with the echocardiogram,