Flow rate across an orifice can be determined from color Doppler echocardiographic maps of the flow convergence region proximal to the orifice. Different methods have been developed in vitro. The proximal velocity profile method was prospectively evaluated in patients with mitral regurgitation. Color Doppler echocardiography was performed in 74 patients before cardiac catheterization. The increasing velocities within the flow convergence region were determined in an apical plane on the straight line from the transducer to the leak; thus the proximal velocity profile was established and plotted on a nomogram. Instantaneous regurgitant flow rate was derived from the position of the resulting curve in relation to the nomogram's reference curves, which were derived from in vitro measurements. Regurgitant stroke volume was calculated as regurgitant flow rate.regurgitant velocity-time integral/regurgitant peak velocity, using additional continuous-wave Doppler. The 55 patients with angiographic regurgitation had a close association between regurgitant flow rate (0 to 600 ml/s) and angiographic grade (Spearman's rank correlation coefficient = 0.91; p < 0.0001). Regurgitant flow rate did not overlap between grades < or = 2+, 3+ and 4+. In 16 patients, regurgitant stroke volume by echocardiography correlated well with that by the angiography/Fick method (r = 0.88; SEE = 17.1 ml), with a regression line close to identity (y = 0.89x + 12.7 ml). The proximal velocity profile method enables determination of mitral regurgitant flow and estimation of regurgitant volume.