The use of a percutaneous cir- culatory assist device may stabilize a patient with acute hemodynamic compromise before the procedure. Prompt mitral valve surgery, preferably mitral repair if possible, is lifesaving in the symptomatic patient with acute severe primary MR. The severity of acute primary MR is variable, and some patients with more moderate amounts of MR may develop compensation as LV dila- tion allows for lower filling pressure and increased for- ward cardiac output. However, most patients with acute severe MR require surgical correction for reestablishment of normal hemodynamics and for relief of symptoms.1 5 This is especially true for a complete papillary muscle rup- ture that causes very severe MR, which is poorly tolerated. 7.2. Chronic Primary MR 7.2.1. Stages of Chronic Primary MR In assessing the patient with chronic MR, it is important to distinguish between chronic primary (degenerative) MR and chronic secondary (functional) MR, as these 2 conditions have more differences than similarities. Pri- mary MR is a disease of the mitral valve apparatus, and secondary MR is a disease of the ventricle or atria. In chronic primary MR, the pathology of 1 of the com- ponents of the valve (leaflets, chordae tendineae, papil- lary muscles, annulus) causes valve incompetence, with systolic regurgitation of blood from the LV to the LA (Table 17). The most common cause of chronic primary MR in high-income countries is mitral valve prolapse, which has a wide spectrum of etiology and presenta- tion. Younger populations present with severe myxo- matous degeneration with gross redundancy of both anterior and posterior leaflets and the chordal appa- ratus (Barlow s valve). A subset of these patients will present with ventricular arrhythmias, mitral annular disjunction, and LV dilation. 