The etiologies of mitral regurgitation (MR) are diverse since the mitral valve apparatus is complex. MR can occur when the mitral valve apparatus is itself diseased (organic MR) or in the absence of any abnormality of the mitral valve apparatus (functional MR). The causes of functional and organic MR are listed in the table below.

Functional MR occurs when the left atrium or left ventricle dilates causing the mitral valve annulus to also dilate thus preventing the mitral valve leaflets from properly coapting. There are many causes of left atrial and left ventricular dilation and the treatment of this type of MR is directed at the primary cause. For example, if a patient develops systolic heart failure with a dilated left ventricle resulting in functional MR, treatment would be directed at the improvement of the heart failure.
Organic MR results from actual disease of the mitral valve apparatus. The mitral valve leaflets, annulus, papillary muscles and chordae tendinae must interact properly for the mitral valve to function properly. Thus, disruption of any of these structures can result in organic MR.