A device for placing in a cardiac valve to assist operation of natural cardiac valve leaflets, the device including a frame for anchoring the device, configured to be placed upstream of the cardiac annulus and shaped to prevent the frame from shifting downstream of the cardiac valve annulus, and at least one anchor extension attached to the frame, the anchor extension configured to extend through the leaflets of the cardiac valve at commissures of the cardiac valve and behind the natural leaflets, preventing the anchor extensions from shifting back from the downstream side of the annulus to the upstream side of the annulus. Related apparatus and methods are also described.
