The correct option is A Ventricle
The chordae tendinae are strong, chord like tendons attached to the leaflets (or cusps) of the atrioventricular valves of the heart. These strings originate from the papillary muscles, which project inward from the walls of the ventricle. When the cusps close, the chordae tendinae prevent them from swinging back into the atrium cavity.
So, the correct answer is option A.