To examine the serial changes of left ventricular output and regional blood flow distribution during the early neonatal period, we measured blood flow volume in the ascending aorta, middle cerebral artery, celiac artery, superior mesenteric artery, and renal artery in 23 normal term infants at 1, 4-8, 24, and 96 h after birth. The blood flow volume in each vessel was measured by the pulsed Doppler technique. In the middle cerebral artery, celiac artery, and superior mesenteric artery, the blood flow volume at 1 and 4-8 h of age was significantly lower than after 24 h of age. In contrast, renal artery blood flow volume did not change significantly throughout the study period. The reduced organ blood flow volume soon after birth was related to a low diastolic blood flow in the major vessels, and the percent diastolic integral of blood flow velocity in each vessel showed an inverse linear correlation with the diameter of the ductus arteriosus. The left ventricular output 1 h after birth was 365 +/- 69 mL/kg/min, which was significantly higher than after 4-8 h of age. Left ventricular output gradually declined to 301 +/- 63 mL/kg/min at 4-8 h of age (p < 0.05 versus 96 h), 272 +/- 48 mL/kg/min at 24 h, and 258 +/- 54 mL/kg/min at 96 h. There was a significant positive correlation between left ventricular output and the ductus arteriosus diameter.(ABSTRACT TRUNCATED AT 250 WORDS)