The leaflets of the av valve are attached to chordeae tendineae that are attached to papillary muscles that are attached to the wall of the ventricle. Therefore, they must be loose inside the ventricle when the av valve is open. When the av valve closes, it is kept from swinging into the atrium by the chordeae tendineae. So, are the papillary muscles there to pull the av valve open after ventricular contraction? Why doesnt the av valve just open passively at this point? And if it does, what would be the point of the papillary muscles?