A device (50; 150; 210) for treating a mitral or tricuspid valve, comprising: a prosthetic sealing element (54; 154) having an axisymmetrical or elliptical top cross-sectional profile, the sealing element (54; 154) dimensioned to be deployed in an annulus of a native mitral or tricuspid valve of a heart at a position between native mitral or tricuspid valve leaflets to contact the native valve leaflets during ventricular systole to create a seal to prevent regurgitation of blood from the ventricle to the atrium, wherein the sealing element (54; 154) comprises a delivery configuration wherein the sealing element (54; 154) is generally elongated and radially collapsed, and further comprising a deployed configuration wherein the sealing element (54; 154) is shortened and radially expanded into an axisymmetrical or elliptical top cross-sectional profile and further dimensioned to permit the native valve leaflets to open and close as the heart beats; and an anchoring element (52; 152; 230) adapted for deployment in the heart, the anchoring element (52; 152; 230) coupled to the sealing element (54; 154) and configured to support the sealing element (54; 154) at the desired position between native valve leaflets, wherein the anchoring element (52; 152; 230) is dimensioned to position the sealing element (54; 154) between the native valve leaflets when the anchoring element (52; 152; 230) is deployed in the heart; wherein the prosthetic sealing element (54; 154) is configured such that a user can actively control expansion of the sealing element (54; 154) to a specifically selected size; and wherein the anchoring element comprises an upper portion and a lower portion, wherein the upper portion and lower portion are configured to be separately deployed. a prosthetic sealing element (54; 154) having an axisymmetrical or elliptical top cross-sectional profile, the sealing element (54; 154) dimensioned to be deployed in an annulus of a native mitral or tricuspid valve of a heart at a position between native mitral or tricuspid valve leaflets to contact the native valve leaflets during ventricular systole to create a seal to prevent regurgitation of blood from the ventricle to the atrium, wherein the sealing element (54; 154) comprises a delivery configuration wherein the sealing element (54; 154) is generally elongated and radially collapsed, and further comprising a deployed configuration wherein the sealing element (54; 154) is shortened and radially expanded into an axisymmetrical or elliptical top cross-sectional profile and further dimensioned to permit the native valve leaflets to open and close as the heart beats; and an anchoring element (52; 152; 230) adapted for deployment in the heart, the anchoring element (52; 152; 230) coupled to the sealing element (54; 154) and configured to support the sealing element (54; 154) at the desired position between native valve leaflets, wherein the anchoring element (52; 152; 230) is dimensioned to position the sealing element (54; 154) between the native valve leaflets when the anchoring element (52; 152; 230) is deployed in the heart; wherein the prosthetic sealing element (54; 154) is configured such that a user can actively control expansion of the sealing element (54; 154) to a specifically selected size; and wherein the anchoring element comprises an upper portion and a lower portion, wherein the upper portion and lower portion are configured to be separately deployed.