BackgroundEstimation of the Mitral valve area (MVA) by planimetry and pressure 1/2 time may be tedious.Mitral leaflet separation (MLS) index is a new method to assess the severity of mitral stenosis and MVA.Aim of this study is evaluation of the MLS index as a measurement for Mitral stenosis. Methods 2D Echocardiography was done in 50 patients with MS in this study:Group1 consisted of 25 patients in sinus rhythm with mean age was 28.6 ± 5.6 years. Four of the patients were male (16%), and 21 were female (84%). Six patients had mild, 13 had moderate and 6 had severe Mitral stenosisGroup II consisted of 25 patients suffering from atrial fibrillation. The mean age was 37.4 ± 9.8 years. Twelve of the patients were male (48%), 13 were female (52%). Three patients had mild,14 had moderate and 8 had severe Mitral stenosisPatients with significant other valvular lesions or heavily calcified Mitral valve were excluded from the study.The MVA was assessed by planimetry and pressure half time. MLS index\was measured in end diastole, as the maximal separation at the tips of mitral leaflets in the parastenal long axis (PLX) and apical 4 chamber (A4C) views.ResultsROC curves for group I demostrated thatIn the PLX view, severe Mitral stenosis was predicted by a MLS of 8.05 mm or less had a 82% sensitivity and 100% specificity for planimetry ( MVA= -.167 +(.162 × MLS), r=.835, p < .001) and MLS of 8.25 mm or less with a 85% sensitivity and 100% specificity for PHT (MVA = -.122 +(.155 ×MLS), r= .753,p < .001)In the apical 4chamber view, severe Mitral stenosis was predicted by a MLS of 7.9 mm or less with a 82% sensitivity and 86% specificity for planimetry (MVA = -.268 +(.176 × MLS), r = .837, p <.001), and 8.25 mm with a 81% sensitivity and 100% specificity for PHT MVA = -.303 +(.177 ×MLS), r = .799, p <.001)ROC curves for Group II demonstratedIn the PLX view, severe Mitral stenosis was predicted by a MLS of 7.25 mm or less with a 89% sensitivity and 90% specificity for planimetry (MVA= -.013 +(.139 × MLS), r= .611, p < .001) and MLS of 7.75 mm or less with a 84% sensitivity and 100% specificity for PHT (MVA = -.203 +(.168 ×MLS), r = .710, p < .001)In the apical 4chamber view, severe Mitral stenosis was predicted by a MLS of 7.65 mm or less with a 89% sensitivity and 100% specificity for planimetry (MVA = -.122 +(.152 × MLS), r = .759, P value <.001) , and 7.9 mm with a 84% sensitivity and 100% specificity for PHT (MVA = -.261 +(.174 ×MLS), r = .840, P value <.001)For both groups MVA by planimetry= -0.304 + (0.052×MLS(PLX view) + (0.125×MLS(A4C view)) , r=0.828; P < 0.001)MLS was significantly different for different degrees of mitral stenosis , and was significantly lower in patients with severe MS compared with mild MS (P < 0.001) , Patients in group I had a mean MLS index of 6.81±1.06 for severe , 9.36±1.33 for moderate and 10.55±0.98 for mild MS in PLAX view. And 7.08 ± 0.55 for severe, 9.03 ± 1.5 for moderate and10.31±0.81 for mild MS in A4C view.Patients in group II had a mean MLS index of 6.76± 0.42 for severe , 8.9±1.16 for moderate and 8.8± 0.76 for mild MS in PLAX view. And 6.53 ± 0.51 for severe, 8.86± 1.24 for moderate and 9.73±0.46 for mild MS in A4C view.Conclusion: The MLS index is a new easy and practical method for assessment of mitral stenosis severity.