AbstractTo assess the growth pattern, relative left ventricular (LV) and right ventricular (RV) sizes, function and volumes, 168 echocardiograms and 14 postmortem hearts of normal human fetuses were studied. LV and RV diameters, atrioventricular valve diameters, wall thicknesses and aortic diameter increased linearly with gestational age from 20 to 39 weeks, but percent changes in ventricular diameters and wall thickness were constant and similar between LV and RV in echocardiograms. The ratios of LV and RV diameters, wall thicknesses and mitral and tricuspid valve diameters were constant and were approximately 1.0 throughout the period studied in echocardiograms and postmortem hearts. LV and RV volumes in postmortem hearts were also similar. LV volumes of postmortem hearts were best approximately by an ellipsoid model, and clinical application of this model to echocardiograms showed a linear increase of LV volume with age and constant ejection fraction and LV output per body weight. These results suggest a linear growth pattern and constant systolic function of the fetal heart, and do not support the concept of RV dominance.