A. chordae tendineae pull the heart valve tightly closed. : These collagenous tendons function to prevent eversion of the atrioventricular valves during ventricular systole. Excessive tension prevents regurgitation rather than causing the displacement seen in prolapse. This mechanism maintains normal valvular competence under high pressure. B. a blood clot blocks the heart valve leaflets. : Thrombus formation on the endocardial surface of a valve is defined as a vegetation or embolism. This mechanical obstruction interferes with laminar blood flow or causes valvular stenosis. It does not describe the structural bulging of the leaflets. C. heart valve leaflets become floppy and bulge backward. : Myxomatous degeneration weakens the connective tissue of the valve leaflets, causing them to move into the atrium during contraction. This redundant tissue leads to superior displacement beyond the annular plane. This is the hallmark anatomical feature of prolapse. D. the heart valve becomes stiff and cannot open. : This condition is medically defined as valvular stenosis, where calcification or fibrosis limits leaflet mobility. It results in narrowed orifices and increased pressure gradients across the valve. This represents a failure of opening, the opposite of prolapse.