To study the hemodynamic effects of graded doses of epinephrine (EPI) in a newborn animal model of hemodynamically significant bradycardia, we performed the following study. Ten newborn lambs were chronically instrumented with catheters and flow transducers so that systemic, pulmonary arterial, left atrial and right atrial pressures as well as heart rate, cardiac output and left carotid artery flow could be monitored. During each of five asphyxia induced bradycardia episodes, with cardiac output depressed to approximately 30% of baseline, lambs were given either 0, 1, 10, 50, or 100 micrograms of EPI in a randomized sequence. After 30 s, the lambs were resuscitated with room air ventilation while hemodynamic parameters were monitored. During asphyxia and prior to EPI administration, all hemodynamic parameters were similar. In addition, for the first 30 s following EPI administration, hemodynamic parameters continued to deteriorate in a manner that was not influenced by the dose of EPI administered. During the resuscitation period with resumption of ventilation, systemic blood pressure and coronary perfusion pressure rose higher following 50 and 100 micrograms/kg of EPI than after the smaller doses. Heart rate was highest following the 100 micrograms/kg dose. Stroke volume and cardiac output, however, appeared to be blunted by the 100 micrograms/kg dose of EPI with no differences in carotid flow noted by dose of EPI administered. It appears that doses of EPI greater than 10 micrograms/kg, the dose currently recommended by the American Heart Association, may be beneficial as an adjunct in treatment of hemodynamically significant bradycardia. However, doses as high as 100 micrograms/kg may blunt cardiac output and stroke volume and should be used with caution.