My personal opinion is that there seems to be a common association between LVDD (Left Ventricular Diastolic Dysfunction) and POTS (Postural Orthostatic Tachycardia Syndrome).
Here’s a good, nay excellent (but long!) video by Dr Paul Cheney on LVDD:-
http://www.cfids-cab.org/MESA/CFS_Dist.htm
For those of you new to the site, you have to cut and paste this link into your browser, to watch it.
Regards
Barbara
(UK)