It has been suggested that flow through a leaking heart valve can be determined by studying the proximal velocity field. Normally, only the centre-line velocity is studied as a potential method. The aim of the study is to improve this method by using information from the entire reconstructed proximal velocity field. Four methods are compared: use of the centre-line velocity; use of velocities at three different angles; integration of velocities over a hemisphere; and integration of velocities over an estimated hemi-elliptical isovelocity line. Measurements are performed in a hydraulic model with 4, 6 and 8 mm circular orifices, and these are compared with those from computer simulation. From the results presented in the study, it is suggested that the velocities should be integrated over a hemisphere within a best zone. This zone is dependent on the instrument settings, but in this case it is positioned 1.2-1.4 orifice diameters from the orifice inlet, with an angle of up to +/- 45 degrees from the centre axis, and contains velocities in the range 0.15-0.45 ms-1.