We examined the utility of three-dimensional (3D) reconstruction of two-dimensional color Doppler images of the proximal jet to quantify the effective area of an orifice in an in vitro model. Steady and pulsatile flows were directed through various orifices; orifice vena contracta areas were quantified with laser flow visualization, thus providing gold standard effective orifice areas. Three-dimensional areas followed vena contracta areas well, although variations in color Doppler gain and 3D gray levels for thresholding produced significant changes in reconstructed images. These variations were minimized by using minimum color gain and 50% gray level threshold. At these settings, 3D areas still overestimated vena contracta areas by approximately 25% because of the poor lateral resolution of the color Doppler system, which caused bleeding of the flow signal past the edges of the proximal jet. Nevertheless, 3D flow images provided a superior format for qualitative and quantitative appreciation of proximal jet shape and dimensions.