A multi-gated pulsed wave color Doppler imaging system is used to provide accurate non-invasive measurements of liquid flow through a narrowed orifice by using the color Doppler to first measure the velocity of flow along an axis perpendicular to the orifice to provide a first image of the liquid velocity. The first image includes a two-color interface at locations in the image representing locations where the liquid velocity is equal to the aliasing velocity of the color Doppler imaging system. The distance from the two-color interface to the center of the orifice is measured and saved. A second image is obtained along an axis perpendicular to the first axis to represent the flow of liquid to the orifice from the perimeter of the orifice. The distance from a two-color interface to the center of the orifice in the second image is measured. The two measured dimensions are used to model a hemi-ellipsoidal surface proximal to the orifice wherein all points on the surface have the same isovelocity. The surface area is multiplied by the aliasing velocity to obtain the volume fluid flow rate through the orifice. A third image can also be obtained along a third axis perpendicular to the first and second axes and used to model an alternative hemi-ellipsoidal isovelocity surface. In a further alternative, a single image can be used to model a panshaped isovelocity surface.