Using Mirabegron to Increase BP in Patients With POTS

Inclusion Criteria: 1. Provision of signed and dated informed consent form. 2. Age \> 18 years old. 3. Documented history of chronic (\> 3 months) of orthostatic intolerance. 4. Diagnosis of syncope or pre-syncope and documented intermittent hypotension unresponsive to conventional life-style modification therapy. 1. A history of syncope (complete loss of consciousness) or presyncope (the sensation that one is about to pass out). 2. At least one documented hypotensive episode with systolic BP \< 90 mmHg on 24-hr ABPM. 3. Inadequate response to conventional therapies. Exclusion Criteria: 1. Patients with other potential etiologies of syncope 1. Sustained tachyarrhythmias other than sinus tachycardia. Specifically, patients with a diagnosis of atrial fibrillation, sustained (\> 30 seconds) arrhythmias including paroxysmal supraventricular tachycardia, atrial flutter, ventricular tachycardia, ventricular fibrillation. 2. Symptomatic bradycardia before pacemaker implantation. 2. Heart failure with either preserved or reduced ejection fraction. 3. Wolff Parkinson-White Syndrome. 4. Stroke within the past 6 months. 5. Any history of myocardial infarction. 6. Active thyrotoxicosis. 7. Any experimental medication concomitantly or within 4 weeks of participation in the study. 8. Patients \< 18 years old because mirabegron is not approved by FDA for use in children. 9. People with a history of allergy to ECG electrodes or adhesive tape. 10. Patients with known contraindications or precautions to mirabegron. 1. Hypertension 2. Severe renal impairment (calculated CrCl \< 30ml/min) 3. Hepatic disease (Child-Pugh Class B) 4. Pregnant or lactation 5. Geriatric patients in long term care facilities 6. Patients who are known to be allergic to mirabegron 7. Patients taking drugs that are CYP2D6 substrates, such as midodrine. An extensive list can be found at the following website: https://drug-interactions.medicine.iu.edu/MainTable.aspx 11. Prisoners