It is sometimes difficult to estimate severity of mitral regurgitation by detecting regurgitant signal using pulsed doppler or color flow mapping. Instead of this, we measured maximum flow velocity at the mitral valve orifice (M. Vel.) using pulsed doppler, and estimated severity of mitral regurgitation. 35 patients of mitral regurgitation were studied, classified into 3 groups according to severity of regurgitation estimated by chest x-p, ECG, and left ventriculography (LVG). Group I: mild mitral regurgitation estimated by chest x-p, ECG and clinical signs without LVG. Group II: moderate mitral regurgitation estimated by LVG (Sellers II). Group III: severe mitral regurgitation estimated by LVG (Sellers III or IV). The M. Vel. (m/sec) of every groups were, 0.88±0.26 in group I, 1.21±0.26 in group II, 1.95±0.32 in group III. According to the severity of regurgitation, the M. Vel. became faster, and statistical differents were recognized among 3 groups. The M. Vel. is less than 1.0 m/sec in normal subjects, but it increases about 2.0 m/sec in group III. So, we suggest that measurements of the M. Vel. is useful and simple in the assessment of severity of regurgitation. Futhermore, M. Vel. × (diameter of mitral valve ring)² using as the index of severity of mitral regurgitation, we recognized more statistical differents among 3 groups. We recommend that a surgical treatment is indicated if this index is above 2,000. A reaon of enlargement of the M. Vel. is not unknown in details, but we consider that the M. Vel. is related with the pressure gradient between LA pressure and LVEDP.