The proximal isovelocity surface area (PISA) method is accurate for quantitating mitral regurgitation but requires recording both mitral maximal and integrated jet velocities using the same continuous-wave Doppler jet signal. In 272 consecutive patients with isolated mitral regurgitation, the mean ratio of maximal to integral of velocity had a narrow range of variation (mean +/- SD, 3.25 +/- 0.47). The estimated regurgitant volume, calculated as regurgitant flow/3.25, showed an excellent correlation with reference regurgitant volumes (r = 0.96 and r = 0.97; standard error of the estimate, 11 ml; both p < 0.0001), with limited overestimation and high sensitivity and specificity for severe mitral regurgitation. The estimated regurgitant volume is a useful measurement in patients in whom the continuous-wave Doppler signal of mitral regurgitation cannot be obtained.