Autoimmune Basis for Postural Tachycardia Syndrome

Inclusion Criteria: * 18-80 years old, female or male * Either healthy control or individual with postural tachycardia syndrome (POTS) defined as heart rate increase \>30 bpm from supine within 10 min of standing, in the absence of orthostatic hypotension (\>20/10 mmHg fall in blood pressure), with chronic symptoms (\>6 months), and in the absence of other acute cause of orthostatic tachycardia * Able and willing to provide informed consent * Understand and be able to comply with the study procedures and restrictions Exclusion Criteria: * Hypertension (\>150 mmHg systolic and \>100 mmHg diastolic) based on history or findings at screening * Orthostatic hypotension (consistent drop in blood pressure \>20/10 mmHg with 10 min of standing) * Cardiovascular disease, such as myocardial infarction within 6 months * History or presence of significant immunological or hematological disorders * History of vagotomy * Currently pregnant women or women planning on becoming pregnant ≤ 3 months * Inability to comply with the protocol * Patients with active implants (such as a cardiac pacemaker, or a cochlear implant) Healthy control subjects will be healthy, non-smoking and on no chronic medications at the time of the study. Healthy control subjects will be group-matched to the POTS patients for age and gender.