When I first had panic attacks and anxiety a couple of decades plus ago, the first thing they told me was that I had mitral valve prolapse. I also worried about it and read and heard scary things at that time. I also had all kinds of scary palps, chest pains, and more. It turns out years later the docs now say I really don't have it, it is so minor its not even considered real MVP (I think the diagnostic criteria may have changed, and it is my understanding that everyone has some degree of not perfect valve closure, at least as we get older). I've been dealing with anxiety and depression yet again for the last year plus, and I know I have triscuspid regurgitation, again minor and nothing of note according to the cardiologist, and not much in the way of mvp. So if the doc tells you its mild, you can be sure the anxiety is causing all the heart symptoms. This time around I haven't had many heart symptoms aside from fairly fast pulse when I am not feeling well (eg anxious and not always even then). I have had rather little in the way of palps this time around (I do get some but not often and no more than before I got sick again), mercifully that aspect seems much less this time.
I was on Lexapro for about a decade at one point and it worked well during that time until the current relapse. It did not bother my heart so you shouldn't fear it or celexa provided the doc says its okay, as Ian said, its not contraindicated for mvp. Incidentally I remember getting attacks of pounding racing heart from my sophomore year in college through my first panic attack illness, then once I got better it never returned even when I got sick again later on. It was aggravated by caffeine and once after a long run. It would literally pound for a minute or two and then suddenly lurch back to normal rhythm. I remember being frightened when it happened, but I got over it when it stopped and it occurred very infrequently. Haven't had one of those in over 2 decades, don't miss it either.
Some of the "symptoms" of mvp and anxiety are similar and sometimes I think the docs don't know which is causing what, again as Ian said there appears to be a link between mvp and anxiety/panic but no one really knows which is the chicken and which is the egg in this situation. The most important thing is to know that when you are on an effective medication for anxiety and its working well, the heart "symptoms" and worry about mvp will disappear, I've had this happen before.