Chordae Tendinae

Strong, fibrous strings, called "chordae tendinae," are attached to the leaflets (or cusps) of the heart on the ventricular side; i.e., the lower chamber. These strings originated from small mounds of muscle tissue, 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 (the upper chamber).