Background: Mitral Stenosis refers to narrowing of the mitral valve orifice, resulting in impairment of filling of the left ventricle in diastole. Proximal isovelocity surface area measurement, also known as the flow convergence method, can be used in transthoracic echocardiography to estimate the area of an orifice through which blood flows. Objectives: To compare simple PISA equation, created by combined fixing the angle to 1000 and the Val to 33 cm/s, with mitral valve area measured by pressure half time and planimetry which was taken as reference method. Patients and Methods: A cross sectional prospective study was conducted in multi teaching centers. Total 104 patients were enrolled in this study from which 41 were excluded from the study. Transthoracic echocardiographic examination was used to analyze parameters selected by M-mode, 2D, and pulse doppler. Results: The patients enrolled in this study were with a mean age of 45.4 ± 7.1 years and 23.8% of them within the age group 30-39 years and the remaining 76.2% were >40 years. Female patients were the dominant represented 73.0% while males were 7.0% of the studied group (female: male ratio was 3:1); 61.9% were in sinus rhythm and 38.1% in atrial fibrillation. About 58.7% of the patients had Wilkin’s score less than 8, the mean mitral valve area according to planimetry method was 1.14 ± 0.32 cm2 and it was 1.12 ± 0.28 cm2 by PISA while the mean mitral valve area by pressure half time method was 1.19 ± 0.30 cm2. The agreement between PISA and planimetry revealed that PISA had good agreement with planimetry in diagnosis of mitral stenosis, (kappa=0.835, P<0.001). On the other hand, there was a fair significant agreement between pressure half time and planimetry. Conclusion: PISA method can effectively predict mitral valve area and severity of mitral stenosis by the equation: mitral valve area = 115 × r2/Vmax, provided that aliasing velocity is fixed at 33 cm/s, with the advantage of easy calculation over other methods used to evaluate mitral valve area by transthoracic echocardiography.