An artificial heart valve for percutaneous delivery comprises: a plurality of support elements comprising a plurality of base segments 50 and a plurality of posts 38； a plurality of flexible leaflets, each attached to two of the posts 38； and one or more strings 26 passing through the support-elements. The heart-valve is configurable between a collapsed delivery configuration and an expanded operational configuration. When the heart-valve is in the collapsed delivery configuration, tensioning string 26 pulls each support-element into engagement with adjacent support-elements until the heart-valve adopts the expanded operational configuration with the support-elements together forming a support structure 32 defining an aperture for blood flow, and in which, the leaflets are movable between open and closed configurations to respectively permit and restrict heart-valve blood flow. Also an artificial heart valve system for percutaneous delivery comprising: the artificial heart-valve as above； and a stent configurable between collapsed delivery and expanded operational states, where string 26 passes through the stent. With the stent in its expanded operational state and the heart-valve in its collapsed delivery configuration, applying tension to string 26 cause the heart-valve to adopt its expanded operational configuration in engagement with the stent.
