Objectives: We aimed to investigate whether coronary sinus (CS) dilatation develops in patients with mitral stenosis (MS) and to demonstrate its relationship with the global myocardial performance of the right ventricle (RV). Methods: We enrolled 34 patients with MS who underwent echocardiography after exhibiting typical symptoms (31 female; mean age 41 +/- 12 years) and 20 age-and sex-matched controls without MS who underwent echocardiography (16 female; mean age 38 +/- 13 years). The RV myocardial performance index (MPI) was detected using tissue Doppler echocardiography (TDE), and maximum CS diameter was measured from the posterior atrioventricular groove in the apical fourchamber view during the ventricular systole. Results: The RV MPI was significantly higher in the MS group compared to the control group (0.60 +/- 0.11 vs. 0.41 +/- 0.08, P < 0.001). Moreover, the maximum CS dimension was higher in the MS group compared to the control group (8.5 +/- 1.1 mm vs. 6.5 +/- 1.4 mm, P < 0.001). The maximum CS dilatation was positively correlated with the RV MPI (r = 0.691; P < 0.001). Conclusion: The RV MPI, which represents both systolic and diastolic functions, is increased in patients with MS and correlates with CS dilatation.