The purpose of this study was to see the relationship between changes in pulmonary venous flow velocities and those in transmitral flow velocities during the first day of life. A serial Doppler echocardiography was performed in 24 normal neonates at 2, 12, and 24 hours of age. The size of the ductus arteriosus was 4.3 +/- 0.5 mm at 2 hours and 2.1 +/- 0.7 mm at 12 hours, and closed in 21 of 24 neonates at 24 hours. The peak systolic pulmonary venous flow (peak S), peak diastolic pulmonary venous flow (peak D), peak D/S, peak velocity at early diastolic filling (peak E), and peak E/A, which were high at 2 hours, decreased significantly at 12 hours but remained constant thereafter. The size of the ductus arteriosus was found to be correlated with peak S, peak D, and peak D/S. There was a direct correlation between peaks E and D (r: 0.64, p < 0.01) as well as a direct correlation between peaks E/A and D/S (r: 0.36, p < 0.05). These results indicate that the diastolic pulmonary venous flow is determined by the same factors that influence the transmitral flow. These waveforms may reflect the increase in pulmonary circulatory volume by left-to-right shunting through the ductus arteriosus.