Thanks for your response Nick. I've had ME for 40 years! I was diagnosed with Epstein-Barr virus in 1986, and was lucky enough to see Dr. Paul Cheney for an obvious diagnosis of MECFS. I'm curious as to whether mitral valve leakage isn't part of a pattern of "Post Exertional Malaise"?
Because I've had ME for so long, I'm a good weathervane. I didn't get heart problems such as unusual and rapid increases in heartbeat, until my early 70s. That's why I think it's part of the degenerative neurological nature of the illness. I hope you get a diagnosis that is appropriate for you, because it does help with research and support.