A Study of Pyridostigmine in Postural Tachycardia Syndrome

Inclusion Criteria:

Diagnosis of postural tachycardia syndrome using the following criteria:

* Orthostatic heart rate increment greater than or equal to 30 beats per minute (bpm) within 5 minutes of head-up tilt.
* Symptoms of orthostatic intolerance. These include weakness, lightheadedness, blurred vision, nausea, palpitations, and difficulty with concentration and thinking.

Both criteria must be fulfilled.

Exclusion Criteria:

* Pregnant or lactating women
* Presence of failure of other organ systems or systemic illness that could affect autonomic function or the patient's ability to cooperate with the study
* Hypothyroidism or hyperthyroidism
* Clinically significant coronary artery disease
* Medications that could interfere with autonomic testing
* Previous treatment with pyridostigmine for POTS. Patients must not have taken pyridostigmine in the past month