Hypercapnia and Orthostatic Tolerance in Postural Orthostatic Tachycardia Syndrome

Inclusion Criteria: * Physician diagnosis of Postural Tachycardia Syndrome (POTS) * Age 18-60 years * Male and Female * Non - smokers. * Able and willing to provide informed consent. * Ability to travel to Libin Cardiovascular Institute of Alberta Autonomic Testing Lab at the University of Calgary, Calgary, AB. Exclusion Criteria: * Overt cause for postural tachycardia, i.e., acute dehydration * Participants with somatization or severe anxiety symptoms will be excluded * Pregnant * Inability to tolerate mask for the duration of the study * Subjects who require portable oxygen at rest or with exercise * Subjects with chronic heart failure or severe pulmonary disease who are unable to climb one flight of stairs due to shortness of breath. * Other factors which in the investigator's opinion would prevent the participant from completing the protocol, including poor compliance during previous studies.