Cardiopulmonary exercise testing is an objective method of assessing the functional capacity of a patient. Also it helps in evaluation of impairment and disability, assessment of exercise-related symptoms especially dyspnea and chest pain and establishment of safety and guidelines for exercise training. Aim: The purpose of this study was Twofold: first to prospectively investigate the effect of surgical correction of mitral regurgitation on ejection fraction, exercise performance and work capacity together with the degree impairment. Second, to assess if the exercise parameters and cardiac function can predict the post operative function class of patients with mitral regurgitation. Methods: This prospective study was carried on 36 patients with rheumatic mitral regurgitation. After surgical intervention, only 23 of them continued the post operative investigation. They were subjected to full history taking with clinical examination, hemoglobin in grams chest x-ray, echocardiography, ventilatory function tests and cardiopulmonary exercise tests. Results: This study showed increased exercise performance after the surgical intervention. There was significant difference concerning VO2max, FC, AT and O2 pulse and subsequently there was improvement in AMA grading and Weber classification. Also we demonstrated that preoperative VO2max, AT, exercise duration and ejection fraction can predict the post operative function class of our patients. Correlation coefficient between preoperative EF and post operative exercise parameters was studied and we found that a contraversery regarding this relation is present. Conclusion: these results indicate that exercise tolerance is improved after corrective surgery for rheumatic mitral regurgitation and there is a contraversery regarding the relation between exercise capacity and left ventricular ejection fraction. Moreover, VO2max, AT, exercise duration and left ventricular ejection fraction are good parameters to predict the post operative functional class of patients with mitral regurgitation.