If you are asking for a single example, mitral stenosis would be one. If you are asking for a definition, an obstructive lesion is any lesion that blocks flow across the valve. This is bad for two reasons. First, it restricts forward blood flow, which can have serious consequences. The second reason is that the blood can back up due to the restriction in forward flow. In the case of mitral obstruction, this can lead to pulmonary edema and CHF. Chronically, this backup can lead to dilation of the atrium and atrial fibrillation or flutter, both of which have their own sequelae.
I am pretty sure that it is mitral stenosis
Heart attacks that damage the structures that support the mitral valve are a common cause of mitral valve insufficiency. Myxomatous degeneration can cause a "floppy" mitral valve that leaks.
The mitral, or bicuspid valve
The mitral valve is closed when the left ventricle is contracting.
Mitral stenosis is the medical term meaning narrowing of the mitral valve.
Mitral valve
Mitral stenosis
Mitral regurgitation is backflow of blood through the mitral valve.
Twice as many women as men are affected by mitral valve stenosis. About 60% of patients with mitral valve stenosis have had rheumatic fever.
The mitral and bicuspid valves are the same thing.
Mitral valve
left atrioventricular valve and left mitral valve
The Mitral valve.