A prosthetic valve assembly for use in replacing a deficient native valve comprises a replacement valve supported on an expandable valve support. The valve support, which entirely supports the valve annulus, valve leaflets, and valve commissure points, is configured to be collapsible for transluminal delivery and expandable contact the anatomical annulus of the native valve when the assembly is properly positioned. Portions of the valve support may expand to a preset diameter to maintain coaptivity of the replacement valve and to prevent occlusion of the coronary ostia.