chest pain

i am 33fem with hashimotos for over 12yrs and mild mvp
with mitral insufficiency.i also suffer from anxiety mainlty heart anxiety.

today i went with my kids to an outdoor gym.
a friend and i started to do power walking.anyway 20 mins later when we slowed down i had a twinge of pain in the middle which didn't last more than a sec but which scared me a lot so i sat down.

20 mins later or so i stared burping what i had eaten earlier producing a very sour taste in my mouth.

i had eaten about 2 hrs before.

could this pain have been indigestion or could it be heart related?

it has never happened before. i had a stress test 2.5 ago and a doppler echo of the heart last year all well.

desperately need yr advice.

pls note i climbed 3 flight of stairs 1 hour after and i did that ok with not even a twinge. i watch my diet, i am not overweight,dont smoke or drink dont have h/disease in my family.had my bloodwork done last year all ok.