Esmolol, a short-acting intravenous cardioselective beta-blocking agent, was evaluated for age-dependent pharmacodynamic and pharmacokinetic features in 17 young patients (6 months to 14 years). A loading dose (500 micrograms/kg/min) alternating with a maintenance dose (25-200 micrograms/kg/min, titrating by 25 micrograms/kg/min every 4 min) was infused until the heart rate or mean arterial pressure decreased 10%. Cardiac index, left ventricular shortening fraction, and systemic vascular resistance were measured at baseline, peak esmolol effect, and recovery. Serum esmolol concentrations were obtained to determine the half-life and the elimination rate constant. Esmolol reduced the heart rate, blood pressure, shortening fraction, and cardiac index in all patients, but it did not change systemic vascular resistance. Maintenance esmolol dose was 118 +/- 49 micrograms/kg/min, and the half-life was 2.88 +/- 2.67 min. Blood pressure and heart rate returned to normal within 2-16 min, but cardiac index and shortening fraction took longer to recover. There were no statistically significant age-dependent pharmacodynamic effects, but blood pressure decreased prior to heart rate and cardiac index took longer to recovery in patients who weighed < or = 15 kg. The pharmacokinetic profile in young patients was similar to that of older patients, but the half-life was shorter. The only side effect was transient nausea and vomiting in one patient. Esmolol is a safe and efficacious beta-blocking agent in young patients.