A valve prosthesis (210; 310; 710; 810) configured to be deployed within a native heart valve, the valve prosthesis (210; 310; 710; 810) comprising: an expandable frame (220; 320; 720; 820) comprising a proximal end (222; 322; 722; 822), a distal end (224; 324; 724; 824) and a longitudinal axis extending therethrough, the frame (220; 320; 720; 820) configured to collapse radially for delivery and to expand radially upon deployment; a distal anchoring feature (234; 734; 834) extending from the frame (220; 320; 720; 820) and expandable from a collapsed configuration to an expanded configuration; a valve body positioned within an interior of the expandable frame (220; 320; 720; 820), wherein the valve body comprises a plurality of leaflets configured to allow flow in a first direction and prevent flow in a second opposite direction; a flap assembly (260; 360; 760) positioned around and secured to an exterior of the expandable frame (220; 320; 720; 820); and characterized in that the valve prosthesis (210; 310; 710; 810) comprises: at least one biasing arm (221; 321; 721a, 721b; 821a, 821b) extending radially outward from the frame (220; 320; 720; 820) when the frame (220; 320; 720; 820) is in an expanded configuration, the at least one biasing arm (221; 321; 721a, 721b; 821a, 821b) being configured to bias the flap assembly (260; 360; 760) radially outward from the longitudinal axis of the frame (220; 320; 720; 820) to provide a space between the flap assembly (260; 360; 760) and the valve body; wherein fluid flow into the space causes the flap assembly (260; 360; 760) to move from a first configuration to a second configuration configured to create a barrier to fluid flow exterior to the frame (220; 320; 720; 820) when the valve prosthesis (210; 310; 710; 810) is deployed within the native heart valve. an expandable frame (220; 320; 720; 820) comprising a proximal end (222; 322; 722; 822), a distal end (224; 324; 724; 824) and a longitudinal axis extending therethrough, the frame (220; 320; 720; 820) configured to collapse radially for delivery and to expand radially upon deployment; a distal anchoring feature (234; 734; 834) extending from the frame (220; 320; 720; 820) and expandable from a collapsed configuration to an expanded configuration; a valve body positioned within an interior of the expandable frame (220; 320; 720; 820), wherein the valve body comprises a plurality of leaflets configured to allow flow in a first direction and prevent flow in a second opposite direction; a flap assembly (260; 360; 760) positioned around and secured to an exterior of the expandable frame (220; 320; 720; 820); and characterized in that the valve prosthesis (210; 310; 710; 810) comprises: at least one biasing arm (221; 321; 721a, 721b; 821a, 821b) extending radially outward from the frame (220; 320; 720; 820) when the frame (220; 320; 720; 820) is in an expanded configuration, the at least one biasing arm (221; 321; 721a, 721b; 821a, 821b) being configured to bias the flap assembly (260; 360; 760) radially outward from the longitudinal axis of the frame (220; 320; 720; 820) to provide a space between the flap assembly (260; 360; 760) and the valve body; wherein fluid flow into the space causes the flap assembly (260; 360; 760) to move from a first configuration to a second configuration configured to create a barrier to fluid flow exterior to the frame (220; 320; 720; 820) when the valve prosthesis (210; 310; 710; 810) is deployed within the native heart valve. at least one biasing arm (221; 321; 721a, 721b; 821a, 821b) extending radially outward from the frame (220; 320; 720; 820) when the frame (220; 320; 720; 820) is in an expanded configuration, the at least one biasing arm (221; 321; 721a, 721b; 821a, 821b) being configured to bias the flap assembly (260; 360; 760) radially outward from the longitudinal axis of the frame (220; 320; 720; 820) to provide a space between the flap assembly (260; 360; 760) and the valve body; wherein fluid flow into the space causes the flap assembly (260; 360; 760) to move from a first configuration to a second configuration configured to create a barrier to fluid flow exterior to the frame (220; 320; 720; 820) when the valve prosthesis (210; 310; 710; 810) is deployed within the native heart valve.