BACKGROUND Supraventricular tachycardia (SVT) occurs frequently in infancy. However, some infants have no recurrences after the initial presentation of SVT, and approximately 30% of infants lose SVT inducibility by 1 year of age. OBJECTIVE To determine whether features at presentation, tachycardia characteristics, or data from an esophageal electrophysiology (EP) study could predict which infants will not require antiarrhythmic medication and which infants will not have inducible SVT at 1 year. METHODS Clinical and tachycardia characteristics at presentation of SVT and data obtained from an esophageal EP study were evaluated prospectively. Patients were followed up for 1 year, and an esophageal EP study was performed to evaluate for continued SVT inducibility. METHODS Primary Children's Medical Center is a tertiary care hospital affiliated with the University of Utah that provides primary care to local patients and is a referral center for a 4-state region. METHODS All infants aged 3 months or younger who presented with SVT between August 1995 and October 1997 were evaluated. METHODS An esophageal EP study was performed at diagnosis and at 1 year. RESULTS The SVT was controlled in all 33 infants. At the initial esophageal EP study, the mechanism of SVT was atrioventricular node reentry in 5 patients (15%) and orthodromic reciprocating tachycardia via an accessory atrioventricular connection in 28 patients (85%). One infant was lost to follow-up, 5 never required medication, 11 had SVT controlled with propranolol hydrochloride, 10 had SVT controlled with amiodarone, and 6 required more than 1 medication. Of the 21 patients who have reached 1 year of age, 16 (76%) were not taking any medication and were free of SVT at the time of follow-up. All 16 patients without clinical SVT have undergone a follow-up esophageal EP study, and 11 of 16 had inducible SVT on esophageal EP study. Thus, of the 21 one-year-old patients, 5 (24%) no longer had clinical or inducible SVT. CONCLUSIONS Control of SVT was possible in all patients. Clinical episodes of SVT were uncommon after discharge, yet most still had inducible SVT at 1 year of age. No data at presentation or initial esophageal EP study were predictive of the clinical course or of continued SVT.