on the partitioning device and a radially expandable reinforcing frame 13 is secured to the proximal or pressure side of the frame 13 as shown in fig1 the ribs 14 have distal ends 15 which are secured to the hub 12 and free proximal ends 16 which are configured to curve or flare away from a center line axis radial expansion of the free proximal ends 16 unfurls the membrane 11 secured to the frame 13 so that the membrane presents a pressure receiving surface 17 which defines in part the productive portion of the patient 39 s partitioned heart chamber the peripheral edge 18 of the membrane 11 may be serrated as shown a continuous expansive strand 19 extends around the periphery of the membrane 11 on the pressure side thereof to apply pressure to the pressure side of the flexible material of the membrane to effectively seal the periphery of the membrane against the wall of the ventricular chamber the ends 20 and 21 of the expansive strand 19 are shown extending away from the partitioning device in fig2 and 3 the ends 20 and 21 may be left unattached or may be secured together e g by a suitable adhesive or the membrane 11 itself while not shown in detail the membrane 11 has a proximal layer secured to the proximal faces of the ribs 14 and a distal layer secured to the distal faces of the ribs in a manner described in co pending application ser.