In order to see whether Doppler parameters from the fetal cardiovascular system change with fetal growth and to compare Doppler values from the various sites, a total of 274 Doppler studies on 73 human fetuses were analyzed. With advancing gestation, the heart rate decreased, the diastolic filling period of both atrioventricular valves increased, and the systolic ejection time of both semilunar valves remained unchanged. Most of the Doppler parameters from the 4 cardiac valves, the aortic arch, the branch pulmonary artery, and the ductus arteriosus increased with increasing gestation. Doppler waveforms from the branch pulmonary artery, the ductus arteriosus, and the aortic arch each had a distinct shape. More study is needed to define the exact relationship between the gestation period and the Doppler parameters and to determine whether Doppler parameters will be useful in assessing fetal heart function.