AbstractBackgroundTolvaptan (TLV) is a selective vasopressin receptor 2 antagonist administered for congestive heart failure (CHF) after inadequate response to other diuretics. The effectiveness and safety of TLV have been evaluated well in adult patients. However, reports on its use in pediatric patients, especially infants, are scarce.MethodsWe retrospectively evaluated 41 children younger than 1 year of age who received TLV for CHF for congenital heart disease (CHD) between January 2010 and August 2021. We monitored the occurrence of adverse events, including acute kidney injury and hypernatremia, as well as laboratory data trends.ResultsOf the 41 infants included, 51.2% were male. The median age when TLV was initiated was 2 months, interquartile range (IQR) 1–4 months, and all infants had been administered other diuretics previously. The median dose of TLV was 0.1 mg/kg/day (IQR, 0.1–0.1). Urine output increased significantly after 48 h of treatment: baseline, 315 mL/day (IQR, 243–394); 48 h, 381 mL/day (IQR, 262–518) , p = 0.0004; 72 h, 385 mL/day (IQR, 301–569), p = 0.0013; 96 h, 425 mL/day (IQR, 272–524), p = 0.0006; and 144 h, 396 mL/day (IQR, 305–477), p = 0.0036. No adverse events were observed.ConclusionsTolvaptan can be used safely and efficiently in infants with CHD. From the perspective of adverse effects, initiating administration at a lower dosage is preferable because this was found to be sufficiently effective.