I'm newly diagnosed but I am reading a book about MVP (it's a bit
dated, but helpful). The guy makes a connection between the mitral
valve malfunctioning and the autonomous nervous system. He says that
is what causes people to have chest palpitation even when inactive or
at rest. The nerves get triggered and don't shut off at the right
time. So maybe that is what is happening when you are exercising. You
get your heart going, releasing hormones and endorphines and your body
gets the timing wrong and kicks into overdrive. I would suggest asking
your doctor and keeping your blood pressure in check. By no means push
yourself to frequently especially if this becomes the norm while you
are exercising. As of yet I have not experienced something of that
nature when I do my 4 day a week workout. I hope you get things worked
out.