This study is researching an experimental drug called REGN7544 (called "study drug"). The study is focused on participants with POTS.

The aim of the study is to see how safe, tolerable, and effective the study drug is.

The study is looking at several other research questions, including:

• How the study drug changes heart rate and blood pressure in participants with POTS
• What side effects may happen from taking the study drug
• How much study drug is in the blood at different times
• Whether the body makes antibodies against the study drug (which could make the study drug less effective or could lead to side effects)
• How the study drug affects symptoms associated with POTS

Key Inclusion Criteria:

1. Is diagnosed with POTS and demonstrates consensus criteria (a), (b), (c) and (d) below during screening:

   1. Increase in HR ≥30 Beats Per Minute (BPM) within 10 minutes of changing from supine to a standing position, as described in the protocol
   2. Absence of orthostatic hypotension, defined as a decrease in Systolic Blood Pressure (SBP) >20 mm Hg within 3 minutes of standing
   3. Absence of other conditions explaining orthostatic tachycardia in the judgment of the investigator, as defined in the protocol
   4. Ongoing episodic symptoms consistent with POTS (for example, lightheadedness, palpitations, tremulousness, generalized weakness, blurred vision, and fatigue) that are worse with standing and are relieved by lying down and which have been present for ≥3 months

2. During screening, a participant must score ≥3 on the Patient Global Impressions of Severity (PGIS)

3. Has a body mass index between 18 and 35 kg/m2, inclusive

Key Exclusion Criteria:

1. History of hypertension or a seated SBP during screening that is >140 mm Hg
2. SBP during Active Stand (AS) test during screening, either supine or standing, that is >140 mm Hg systolic on ≥2 measurements
3. Increase in HR <20 BPM within 10 minutes of changing from supine to a standing position, as defined in protocol
4. Is judged by the investigator to have significant heart failure, cardiovascular disease, liver disease, or renal disease (ie, estimated Glomerular Filtration Rate (eGFR) <60 ml/min/1.73m2) based on medical history, physical exam, laboratory studies, and/or electrocardiogram (ECG) performed during screening period
5. Is confined to bed more than 50% of waking hours
6. Within 5 days of screening visit has used medications with direct effects on blood volume, BP, or HR (eg, midodrine, droxidopa, octreotide, clonidine, methyldopa, ivabradine, beta-blockers, calcium channel blockers, pyridostigmine, fludrocortisone, desmopressin, stimulants or intravenous (IV) saline)

NOTE: Other protocol-defined inclusion/exclusion criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing.

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf