Hi Sissy,
I'm afraid I have no idea what is going on with you, but you are doing exactly what you should be.............consulting with your doctors.
You first saw a cardiologist who did tests, which all turned out normal, aside from the small MVP. What did he/she have to say about your tachycardia?
Then you saw your OB/GYN..............did you not ask him/her if this was affecting your baby? If not, WHY NOT? Why would you get on this forum and ask a group of non-medical people if this was affecting your baby? Why would you think WE would know more than your OB?
You are now going to see a pulmanologist and have a chest X-ray. This is good, and will hopefully and finally give you the answer you are seeking.
There may be others on this forum who have experienced what you are going through, and if so, I hope they respond to your concerns. I'm sorry this was not as reassuring as you had probably hoped it would be, but we are not doctors here. You are doing exactly what all of us would tell you to do...............see your docs!
I wish you and your baby the very best outcome. Please let us know what you find out. We care very much.
Peace
Greenlydia