Additional Study Information: The purpose of this research is to see if an experimental drug called REGN7544 is effective to treat individuals with postural orthostatic tachycardia syndrome (POTS). REGN7544 is an antibody. An antibody is a kind of protein that your immune (defense) system normally makes to fight bacteria and viruses in your body. Scientists can now make antibodies in the laboratory and produce them for the treatment of many different diseases. REGN7544 is designed to bind to a cell protein called natriuretic peptide receptor 1 (NPR1), which is found on the surface of different types of cells in the body. Blocking the activity of the NPR1 is expected to increase blood volume and/or blood pressure. The study drug is not approved by any public health agency for any kind of treatment, and is therefore considered to be an investigational drug. If you qualify for the study, you will be randomly assigned to 1 of 3 cohorts (groups), each consisting of about 27 participants. You will have a 67% (2 out of 3) chance of being assigned to a group that will receive REGN7544 and a 33% (1 out of 3) chance of being assigned to a group that will only receive placebo. A placebo looks like a treatment but does not contain any real medicine. You will not know which group you have been assigned and your study team will not know either. You will be in the study for about 18 weeks. During the study, you will be administered the study drug by subcutaneous injection, have your blood drawn by intravenous (IV) line placement, and have your blood pressure measured.