We used pulsed Doppler echocardiography to study the right ventricular diastolic function of29 normal babies and 12 neonates with pulmonary atresia and intact ventricular septum. Eleven patients underwent staged operations of closed pulmonaryvalvotomy followed by either rightventricular outflow reconstruction (n=5) or balloon angioplasty of the pulmonary valve (n=3). In normal babies, the Doppler wave form showed dominant early (E) and separate late active (A) waves of activity, when the heart rate was slow (<100/min). The two waves gradually merged with increasing heart rate, to form a monophasic active wave. Prior to any intervention, all except one of our patients had only a monophasic active right ventricular filling wave over the entire range of heart rates recorded. To quantitate these differences in ventricular filling, we derived 4 diastolic indices from the ratio of: the peak velocity of the early versus the late active wave (EIA); the integral with time of these waves (E/Aarea); the time of diastolic filling relative to the cardiac cycle (TIRR); and the peak diastolic filling velocity relative to the mean filling velocity over the cardiac cycle (Velocity Index). Profiles of the indices against heart rate for both normal controls and patients indicated that only the index of the time of diastolic filling (T/RR) and the Velocity Index were appropriate for our serial comparisons. Thus, for neonates with pulmonary atresia, the index of the time (TIRR) was significantly lower (0.29±0.03 vs 0.43±0.04, p<0.01) and the Velocity Index higher (5.98±0.79 vs 3.98 ±0.31, p<0.001) than those of normal. After valvotomy, but with a poor surgical result, babies continued to have a predominantly monophasic right ventricular filling pattern without significant improvement (p>0.05) of the index of time (T/RR=0.29±0.05) or velocity (5.88±1.17). Babies who underwent a second stage procedure and achieved a final good result had predominantly biphasic right ventricular diastolic filling waves with significant progression (p<0.001) in the index of time (T/RR=0.42±0.03) and velocity (4.09±0.49).