Clinical Research Directory

Inclusion Criteria: * Physician Diagnosis of POTS as defined by the CCS Consensus Statement and as follows: * Sustained, excessive orthostatic tachycardia ≥ 30 bpm within 10 minutes standing. * Absence of orthostatic hypotension (\>20/10 mmHg decrease) within 3 minutes standing. * Chronic orthostatic symptoms that improve with recumbence. * Age 18-60 years old. * Ability to attend the Calgary Autonomic Research Clinic in Calgary. * Resident of Canada Exclusion Criteria: * Overt cause for postural tachycardia (i.e., acute dehydration, thyroid disease) * Participants with somatization or severe anxiety symptoms will be excluded * Pregnant (self-reported) * Underlying causes of tachycardia including acute hypovolemia, endocrinopathy, anemia, anxiety, medication effects, recreational drug effects, and prolonged bedrest. * Other factors which in the investigator's opinion would prevent the participant from completing the protocol, including poor compliance during previous studies * Fludrocortisone use (due to effects on renal Na+ handling) * Patients who have received IV saline in the 2 months preceding the study or who plan to receive it during the course of the study