Background: The aim of this study was to evaluate the reliability of peak mitral inflow (E-wave) velocity, which was thought to be easier and more practical than qualitative and quantitative methods used to grade mitral regurgitation (MR) in patients both with normal and low left ventricular (LV) ejection fraction (EF). It is known that peak E-wave velocity increases in MR. But correlation of this increase with regurgitant fraction (RF), its usefulness in grading MR, and the effect of EF on peak E-wave velocity have not been studied in detail. Methods: We prospectively examined 135 consecutive patients with varying grades of MR with echocardiography. MR was evaluated both qualitatively and quantitatively, and concordance of these 2 methods was determined. Peak E-wave velocity, A-wave velocity, and E-wave deceleration time were measured and the E/A ratio was calculated. LV isovolumetric relaxation and contraction times were measured. Different MR groups classified by RF were compared with each other. Results: Concordance of quantitative and qualitative evaluation was low in patients with low EF (κ 0.37 vs 0.65). Peak E-wave velocity and E/A ratio showed significant differences between MR groups. Peak E-wave velocity correlated with the RF and EF (r = 0.47, r = 0.33, respectively, P < .001). Sensitivity, specificity, and negative predictive value of peak E-wave velocity >1.2 m/s suggesting severe MR were found to be different in patients with normal and low EF (96% vs 66%, 78% vs 83%, 97% vs 78%, respectively). E-wave deceleration, LV isovolumetric relaxation, and contraction time did not show a correlation with RF. Conclusion: Peak E-wave velocity is a screening method that could be used in common for determining severity of MR semiquantitatively, especially in patients with normal EF.