Myxomatous degeneration of the mitral valve leaflets and chordae tendineae is the primary cause, leading to redundant, thickened, and “floppy” valve tissue. This causes the leaflets to bulge (prolapse) into the left atrium during systole.
It’s the most common cause of primary mitral regurgitation (MR) in developed countries.
Any activity that decreases the left ventricular volume (e.g. standing) will exaggerate the tendency for prolapse. Thus the click and the murmur moves closer to S1.
Any activity that increases the left ventricular volume (e.g. squatting) will decrease tendency for prolapse. Thus the click and the murmur moves close to S2, or not happen at all.
