The mitral valve has two leaflets, or flaps, that open when the
heart relaxes (diastole) and close when it contracts (systole). The base of
each leaflet is attached to the heart muscle—the myocardium—by strong, flexible
cords called the chordae tendineae, which control the opening and closing of
the mitral valve. The chordae are thin and white. Their appearance is often
compared to the strings of a parachute.
The chordae attach to the papillary muscles, a group of muscle fibers
in the myocardium. These muscle fibers are located inside the lower left
chamber (left ventricle) of the heart.