Which structure is responsible for maintaining atrio-ventricular valve closure in the heart?

Purkinje fibers are components of the cardiac electrical conduction system and have no mechanical role in maintaining valve closure.

The foramen ovale is a fetal interatrial opening that typically closes after birth and has no role in AV valve function.

Papillary muscles are specialized myocardial projections that attach to the cusps of the mitral and tricuspid valves through the chordae tendineae. When the ventricles contract, the papillary muscles simultaneously contract, maintaining tension on the chordae tendineae and preventing the valve leaflets from inverting back into the atria, thereby ensuring AV valve closure and preventing regurgitation.

Cardiac myocytes are general contractile cells of the myocardium and are not specialized structures responsible for AV valve closure specifically.