The aim of this study was to evaluate the changes in Doppler transmitral flow patterns during the 1st d of life. Doppler echocardiography of the ascending aorta and mitral valve was performed serially in 20 normal neonates at 2, 12, and 24 h of age. A computer-interfaced digitizer pad was used to measure the following: ascending aorta flow velocity-time integral, total diastolic filling flow velocity-time integral, flow velocity-time integral of early diastolic filling, and flow velocity-time integral of atrial contraction. The inner diameter of the ductus arteriosus was 4.2 +/- 0.6 mm at 2 h of age, 2.3 +/- 0.5 mm at 12 h of age, and had closed in 17 of 20 neonates (85%) by 24 h of age. The ascending aorta flow velocity-time integral and total diastolic filling flow velocity-time integral, which were high at 2 h of age, decreased significantly at 12 h of age [12.2 +/- 2.1 cm versus 9.6 +/- 1.7 cm (p < 0.001) and 8.0 +/- 1.1 versus 7.1 +/- 1.4 (p < 0.01), respectively] but remained constant thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)