One potential cause of valve dysfunction is rupture of the chordae tendineae why would this lead to valve dysfunction

Rupture of the chordae tendineae can lead to valve dysfunction because it makes the valve prolapse.

When the pressure is increased, the valve in ventricle will be pushed and close the hole that leads to the atrium. Chordae tendineae is supporting the heart valve by pulling it, making it look like a opened parachute. Without chordae tendineae the hole will not be closed completely.