Why Does Mitral Valve Prolapse Murmur Increases with Valsalva

The Valsalva maneuver will increase the intensity of the murmur due to the decrease in preload to the right side of the heart, resulting in decreased left ventricular end-diastolic volume (the same is seen with standing from a squatting position).

How does Valsalva affect MVP?

Both Valsalva maneuver and standing decrease venous return to the heart thereby decreasing left ventricular diastolic filling (preload) and causing more laxity on the chordae tendineae.

Why does murmur decrease with Valsalva?

By decreasing left ventricular filling, the left ventricular outflow tract obstruction worsens, making the murmur louder. In patients with aortic valvular stenosis, the murmur will get softer with Valsalva/standing because less blood is being ejected through the aortic valve.