A frame assembly (222) includes a tubular portion (32) that defines a lumen along an axis; a plurality of arms (46) coupled to the tubular portion at a first axial level, each of the arms extending radially outward from the tubular portion to a respective arm-tip; and a plurality of ventricular legs (50) that are coupled to the tubular portion at a second axial level, and that extend radially outward from the tubular portion. A first sheet (440) has a greater perimeter (446), and a smaller perimeter (448) that defines an opening. The first sheet is stitched onto the plurality of arms, with the opening aligned with the lumen. Subsequently, an outer perimeter (454) of a second sheet (450) is stitched to the greater perimeter of the first sheet. Subsequently, the second sheet is everted by passing an inner perimeter (452) of the second sheet around the arm-tips.