Abstract: A replacement heart valve is configured to replace a native atrioventricular heart valve (mitral or tricuspid valve, positioned between an atrial chamber and a ventricular chamber). The replacement valve includes a a thin and flexible wall portion having no more than two leaflets. Two securement locations adjacent the outlet end of the valve are adapted to be attached to respective papillary muscles. The unconstrained regions between the securement locations flex inwardly into and out of engagement with each other in response to blood pressure in order to close and open the valve. The leaflets engage each other along a line of commissure.