['To determine the effects of muscle paralysis on aortic root blood flow in preterm infants with hyaline membrane disease.', 'Each patient served as his/her own control in a prospectively controlled trial.', 'Neonatal ICU in a university hospital.', 'Ten ventilator-dependent preterm infants weighing 800 to 2820 g, 0 to 8 days of age, with hyaline membrane disease and seven control patients.', 'Noninvasive measurement of aortic root blood flow by Doppler echocardiography 30 min before and 60 min after respiratory paralysis with 0.1 to 0.5 mg/kg of iv pancuronium, or following ventilator changes in control subjects.', 'Mean aortic root blood flow increased significantly (p less than .001), from 212 to 276 mL/min.kg, accompanied by significant increases in stroke volume and heart rate.'] Does aortic root blood flow increase after pancuronium in neonates with hyaline membrane disease?