The mitral valve is a complex anatomical structure opening in the left main compartment during the filling phase (diastole) and is closed through the ejection phase (systole). Mitral regurgitation (leakage) is the most common cardiac valvular abnormality and caused by any disease of the flap apparatus (primary) or disease of the heart's left main chamber and / or pre-chamber (secondary). The most common reason for primary mitral regurgitation is mitral valve prolapse where the free edge of a mitral leaflet slips past the other which results in a closure defect during systole. The purpose of this study was to review the current literature about the condition and the most common surgical method used for prolapse repair. Moreover, the author wanted to analyze a large current patient material from OUS Ullevål where the method has been introduced in Norway and used for over 30 years. Medical records of all patients treated with mitral valvuloplasty according to the thoracic surgery registry in the years 2005 to 2008 were reviewed. Literature study confirms that mitral valve prolapse is a well-known and common cause of mitral regurgitation, and that surgical repair today is possible in many cases. The evaluation of mitral valve prolapse includes various diagnostic modalities where cardiac ultrasound (echocardiography) has a central role. Review of patient records show that 70 patients were operated in this 3-year period. After 5 years 13 of them had died. Patients who died were older, had poorer kidney function and higher inflammation samples (eg. CRP). The author concludes that mitral valve prolapse is a relevant valve disease which can be treated with a reparative surgery in most patients. Results from OUS Ullevål show that treatment is on par with international centers and patient-related factors is important for survival.