Aim: To assess the reproducibility of, and determine normative data for, flow volume measurements from the right common carotid artery (CCA) and its relation to left ventricular output (LVO) in stable term and preterm babies using Doppler ultrasound. Methods: Right CCA flow volume was measured using a near focus, hig h frequency transducer by obtaining intensity weighted mean velocity and right C CA diameter. LVO was determined using standard Doppler techniques. Reproducibili ty studies were performed on 30 newborn infants by two observers. Normative data were obtained from 40 spontaneously bre athing preterm babies and 21 term babies. Results: The intraobserver coefficient of variation for CCA flow measurements was 10.5%for observer 1 and 15.4%for o bserver 2, whereas the interobserver coefficient of variation was 16.4%. In ter m and preterm infants, right CCA flow was about 20 ml/kg/min, accounting for 11 %of cardiac output. Among the preterm infants, there was a positive correlation of right CCA flow with gestation (r = 0.61, p < 0.001), weight (r = 0.64, p < 0 .001), and LVO (r = 0.59, p < 0.001). Right CCA diameter also increased with wei ght (r = 0.63, p < 0.001) and gestation (r = 0.58, p < 0.001). The proportion of LVO distributed to the right CCA did not increase with gestation, nor did the r ight CCA flow per kg body weight. Conclusions: It is possible to perform reprodu cible measurements of flow volume in the CCA of newborn infants. In stable, spon taneously breathing babies, both cardiac output and carotid flow increased with gestation and body weight. The proportion of cardiac output distributed to the r ight CCA remained relatively constant across gestation. Aim: To assess the reproducibility of, and determine normative data for, flow volume measurements from the right common carotid artery (CCA) and its relation to left ventricular output (LVO) in stable term and preterm babies using Doppler ultrasound. Methods: Right CCA flow volume was measured using a near focus, hig h frequency transducer by obtaining intensity weighted mean velocity and right CAV diameter. LVO was determined using standard Doppler techniques. Reproducibili ty studies were performed on 30 newborn infants by two observers. Normative data were obtained Results were: 40 spontaneously bre athing preterm babies and 21 term babies. Results: The intraobserver coefficient of variation for CCA flow measurements was 10.5% for observer 1 and 15.4% for o bserver 2, whereas the interobserver coefficient of variation was 16.4%. In ter m and the preterm infants, right CCA flow was about 20 ml / kg / min, accounting for 11% of cardiac output. Among the preterm infants, there was a positive correlation of right CCA flow with gestation (r = 0.61, pO.001), weight (r = 0.64, pO.001), and LVO (r = 0.59, pO.001). Right CCA diameter also increased with wei ght r = 0.63, p <0.001) and gestation (r = 0.58, p <0.001). The proportion of LVO distributed to the right CCA did not increase with gestation, nor did the right CCA flow per kg body weight. Conclusions: It In stable, spontaneously breathing babies, both cardiac output and carotid flow increased with gestation and body weight. The proportion of cardiac output distributed to the right CCA remained relatively constant across gestation.