Tendinous cords

Each of the semilunar cusps of the atrioventricular valve (mitral and tricuspid) is attached to several strands of connective tissue, the chordae tendineae (tendinous cords), sometimes referred to as the heart strings. They are composed of approximately 80 percent collagenous fibers with the remainder consisting of elastic fibers and endothelium. They connect each of the cusps to a papillary muscle that extends from the lower ventricular surface.