POTS IS an autonomic disorder under the general heading of Dysautonomia (which involves many other different types of orthostatic intolderance). Though it involves the heart few patients actually have heart defects. And the "Grinch" article has long been proven wrong; there are lots of new articles and studies being written which you can check out at dinet.org. Cardiologists, Rheumatologists, Endocrinologists, Neurologists, Electrophysiciologists...all these types of doctors diagnose this disorder and treat it. The most common way to dx is with a Tilt Table Test (TTT) and a sweat test (as patients often have abnormal sweating). Every patient salt loads and typically takes a med, like Florinef, to raise their BP if it's tolerable...lots of patients have a difficult time tolerating meds.
POTS specifically affects the autonomic system causing blood pressure and heart rate to not match meaning the heart rate typically jumps past 120 bmp and blood pressure doesn't rise appropriately with it, often falling which is what causes the patient to pass out. But that's only a portion of the problem, autonomic dysfunction also causes additional issues such as motility, breathing, cerebral hypoxia, temperature, crippling fatigue, pain, blood pooling.... I could go on for pages.
Sure it's easy to say it's a "heart problem" for a layman's term but it's SO much more and rather insulting, to those of us who suffer from this disabling condition, not to include the correct information. Again, visit dinet.org for proper details.