Introduction. Animal studies and rare human studies have suggesteda negative effect of barbiturates on cardiac function. Althoughintravenous (IV) phenobarbital is used routinely in children in theclinical setting, studies in children are lacking. We performed a studyto evaluate effect of IV phenobarbital loading on myocardial systolicfunction of children.Methods.xIn a prospective pilot study in children without congenitalheart defects, the effect of IV phenobarbital was evaluated on theleft ventricular systolic function measured by ejection fraction (EF)by Simpson’s method via an echocardiogram. Any child less than 18years of age who received IV loading dose of at least 20 mg/kg ofphenobarbital given as an infusion over 20 - 30 minutes for variousmedical indications was eligible to take part in the study. Three measurementsof EF by an echocardiogram were made: before loadingdose, 30 minutes after completion of the loading dose, and prior tothe first maintenance dose. Relevant clinical data were recorded,including vital signs, immediately prior to each echocardiogram.Change of function as measured by EF over time was analyzed usinglinear mixed modeling methods. For this study, significant change inblood pressure was defined as a drop of at least 20 mmHg in systolicblood pressure.Results. Ten children (70% female, age range two days to 8.2 years)were enrolled. Three had hypotension with a drop of systolic bloodpressure greater than 20 mmHg from baseline. On examining thetrajectory of EF on each individual graphically, the left ventricularEF tended to fall immediately following phenobarbital therapy andreturn to baseline on re-evaluation. These trajectories were statisticallysignificant for EF.Conclusions. Phenobarbital had a direct and transient depressanteffect on systolic function of the myocardium in one third of the cases.The depression in EF appeared to be transient with return to baseline in less than 24 hours. We recommend close monitoring with anticipationof decreased function in children when using IV phenobarbital.Kans J Med 2019;12(2):40-44.