This study is a randomized, double blind, placebo-controlled study to assess the efficacy of a single iron sucrose infusion in adolescents with non-anemic iron deficiency and POTS. Subjects will be screened at outpatient clinic visit appointments. Interested qualified subjects will be consented and offered participation in this trial. Once consent and assent (for patients less than 18 years of age) has been obtained, subjects will be randomized to either treatment or placebo group. Subjects will participate in two on site study visits. During the first visit subjects will complete baseline laboratory studies, tilt table test and study questionnaires. Subjects will then receive the intervention study drug or placebo. The second study visit will occur 7 days + 2 days from the first study visit. During the second study visit subjects will repeat laboratory studies, tilt table test and study questionnaires. Follow up questionnaires will be sent to all subjects six months following the initial study visit.