The effect of aortic outflow on the quantification of mitral regurgitation by the flow convergence method was investigated by both in vitro experiments and computational simulations. Digital analysis of the color Doppler M-mode images was compared with results obtained with laser Doppler anemometry, an engineering gold standard, and three-dimensional computational simulations. Regurgitant orifices of 3.2 and 6.4 mm in diameter were used with instantaneous aortic flow rates from 0 to 500 ml/sec, corresponding to net cardiac outputs of 0 to 5 L/min. In the absence of aortic outflow, a clear plateau was observed in plots of the calculated flow rate as a function of the distance from the orifice, indicating that there was a zone in which the hemispheric assumption was valid. As the aortic outflow was increased, the length of this plateau region decreased and then disappeared at high aortic flow rates. Farther from the orifice, beyond the plateau zone, the flow rate was overestimated and this overestimation increased with increasing aortic flow rate. Results showed excellent agreement between in vitro experiments and computational stimulations. This study demonstrated that aortic outflow has a dramatic effect on the flow convergence region and therefore must be considered in flow rate calculations.