Pathophysiology
The Mitral valve is closed during systole to allow blood to continue its travel out through the Aorta and into the body. The audible murmur is turbulence caused by backflow of blood back through the improperly closed or damaged valve. The regurgitation is most frequently holosystolic and starts immediately after S1, and continues with a relatively flat, harsh/blowing murmur throughout systole.

 Mitral Regurgitation can be acute or chronic:

 Chronic MR has in the past been associated with Rheumatic Heart Disease which with widespread use of antibiotics is now rarely found in Western countries. In developing countries however, this may still be a leading cause, affecting very often children.

In Western countries today, the most common cause of MR is Mitral Valve Prolapse, which today accounts for almost half of all cases. Other causes may be(*) :

- Ischemia
- Mitral annular calcification

- Left ventricular dilatation
- Tendineae rupture
- Papilllary muscle dysfunction

In rare cases other causes may be:

- Ehlers-Danlos syndrome
- Mrfan syndrome

- Osteogenesis imperfecta
- Systemic lupus erythematosus

Acute MR is in most cases caused by a spontaneous chordae tendineae rupture secondary to myocardial infarction, or sudden strenuous efforts i.e. from heavy lifting etc.

Depending on the size of the  ruptured chorda, volume overload on the left ventricle, resulting in elevated atrial pressure may cause pulmonary edema and dyspnea. Sudden death may occur in serious cases. However, patients may remain with minimal symptoms and prognosis is quite good. If the acute stage is tolerated, chronic MR is developed. 

 *)  www.emedicine.com/EMERG/topic314.htm