To determine the hemodynamic responses to dopamine and epinephrine infusions in newborn piglets during normoxia and hypoxia. Prospective, randomized, blind cross-over study. Newborn piglets (n = 7). Animals were acutely instrumented for measurements of cardiac output, pulmonary and systemic pressures, carotid and coronary artery blood flow, and coronary artery oxygen consumption. Dopamine at infusion rates of 2 to 16 micrograms/kg/min and epinephrine 0.2 to 1.6 micrograms/kg/min were administered during normoxia. Six piglets were similarly prepared and were then made hypoxic to an arterial O2 saturation of 45% to 50%. Epinephrine at infusion rates of 0.2 to 3.2 micrograms/kg/min and dopamine at rates of 2 to 32 micrograms/kg/min were administered in random order during hypoxia. During normoxia, cardiac output increased similarly with both drugs and was significantly increased by > or = 0.2 micrograms/kg/min of epinephrine and significantly increased by 8 or 16 micrograms/kg/min of dopamine. Mean arterial blood pressure was not affected by dopamine but was significantly increased by epinephrine at a rate of 1.6 micrograms/kg/min. The relative effects of the drugs on pulmonary and systemic vascular resistance differed, the pulmonary/systemic vascular resistance ratio was reduced at the higher doses of epinephrine (i.e., 0.8 and 1.6 micrograms/kg/min) and was unaffected by dopamine. Coronary artery oxygen consumption and coronary blood flow increased significantly with both medications at rates > 0.4 and 4 micrograms/kg/min, respectively. Increases of both variables were greater with epinephrine than with dopamine. Myocardial extraction ratio was unaffected by dopamine and reduced at 0.2 and 1.6 micrograms/kg/min of epinephrine. Hypoxia caused significant increases in cardiac index, systemic blood pressure, pulmonary arterial pressure, carotid artery blood flow, coronary artery blood flow, coronary oxygen consumption, coronary oxygen extraction ratio, and the pulmonary/systemic vascular resistance ratio. Mean systemic arterial blood pressure increased significantly with 1.6 and 3.2 micrograms/kg/min of epinephrine, but was not significantly affected by dopamine at any infusion rate. Cardiac index was not affected significantly by either of the medications. Thus, there was a significant increase in the calculated systemic vascular resistance index with the highest dose of epinephrine, in contrast to the slight, statistically significant, decrease in calculated systemic vascular resistance index with the highest dose of dopamine. Epinephrine significantly reduced pulmonary arterial pressures at 0.2, 0.4, and 0.8 microgram/kg/min. Dopamine had no effect on this variable. The pulmonary/systemic vascular resistance ratio was significantly reduced by epinephrine at doses of 0.2 and 3.2 micrograms/kg/min, whereas the highest dose of dopamine caused a significant increase in the pulmonary/systemic vascular resistance ratio. Epinephrine infusion during normoxia increases systemic pressure more than pulmonary arterial pressure at doses > or = 8 micrograms/kg/min, and furthermore, produces a more appropriate hemodynamic profile in the presence of hypoxic pulmonary hypertension than dopamine infusion, in the acutely operated anesthetized piglet.