Abstract: The combination of a prosthetic valve and a sinus. The valve has a plurality of flexible leaflets for opening and closing the valve, each leaflet having an edge region attached to a frame of the valve and further having a free edge. The sinus has a plurality of lobes symmetrically disposed around the periphery of the sinus, and a conduit located downstream of said lobes in the direction of blood flow through the sinus. The sinus is such that the valve may be located therein with said attached edges of any one of the leaflets extending in coincidence with an upstream edge region of a respective lobe, wherein in axial section taken centrally through a lobe.