The purpose of this study was to evaluate the feasibility of three-dimensional freehand echocardiographic assessment of ventricular volumetry in healthy fetuses and in fetuses with congenital heart disease. The study was approved by the hospital institutional review board. After echocardiographic examination by conventional ultrasonographic equipment interfaced with a magnetic tracking system, three-dimensional cardiac data were collected prospectively in 57 fetuses. Ventricular volumes were determined from three-dimensional data sets, and 22 fetuses with congenital heart disease were compared with 29 healthy fetuses. A multiple regression analysis of covariance was performed to assess between-group differences. Gated three-dimensional volume data sets enabled assessment of ventricular volumes in 51 of the 57 fetuses. Both fetuses with and without congenital heart disease had exponential increases in cardiac volumes during gestation. In fetuses with congenital heart disease and a marked inequality of ventricular size but no heart failure, the combined end-diastolic and stroke volumes of both ventricles were found to be significantly reduced compared with controls with no disease and fetuses with other types of congenital heart disease. Three-dimensional imaging can provide estimates of ventricular volume changes in fetal hearts with abnormal ventricular morphology that cannot easily be performed by two-dimensional echocardiography, and it may provide insight into evolving congenital heart disease.