Purpose: The aim of this study was to evaluate the reliability of mitral regurgitation color M-mode regurgitant flow propagation velocity (RFPV) in grading mitral regurgitation (MR). Methods: We prospectively examined 52 consecutive patients with grades of MR mild in 10 patients, moderate in 19 patients, and severe in 23 patients with quantitative pulse Doppler echocardiography. MR was evaluated by vena contracta diameter (VCD), regurgitant jet area (RJA), and RFPV. These qualitative and quantitative methods were compared with the pulsed Doppler quantitative flow measurements and concordance of these three methods was determined. Results: The mean RFPV for mild, moderate, and severe MR were 26.4 +/- 7 cm/sec, 43.3 +/- 7 cm/sec, and 60.3 +/- 7.3 respectively (P < 0.001). RFPV is highly sensitive and moderately specific in differentiating mild and severe MR from other subgroups. Sensitivity and specificity were 92.1%-64.3% for mild and 100%-68.5% for severe MR, respectively. Significant correlation was observed between pulse Doppler quantitative grades, RFPV, VC, and RJA (P < 0.0001, r = 0.87; P < 0.0001, r = -0.84, P < 0.0001, r = 0.76, respectively). Conclusion: This results show that RFPV is a reliable and simple semiquantitative new method that can be used for determining severity of MR.