A replacement heart valve, comprising: a valve body (330; 630) comprising an outer layer and an inner layer; the outer layer being tubular and having a longitudinal axis, an upstream end and a downstream end, the inner and outer layers formed from a thin, flexible material, wherein the thin, flexible layer is not substantially longitudinally stretchable; the inner layer being generally tubular, having a longitudinal axis generally collinear with the outer layer, and being positioned within the tubular outer layer, the inner layer formed from said thin, flexible material and defining a plurality of leaflets adapted to move between an open state and a coapted state, each leaflet having a side edge and a downstream portion, adjacent leaflets of the inner layer being connected by a commissural portion (360, 361; 660, 661); wherein the leaflets are attached to the outer layer along the leaflet side edges, and the commissural portions (360, 361; 660, 661) are attached to the outer layer downstream of at least a portion of the leaflet side edges; and an elongate stent that can be radially compacted to a compacted state and radially expanded to an expanded state, the stent made up of a plurality of struts and having a longitudinal axis, characterised by the stent having a foreshortening portion and a non-foreshortening portion, the foreshortening portion being configured so that as the stent is radially compacted, the foreshortening portion longitudinally expands, and as the stent is radially expanded, the foreshortening portion longitudinally contracts, the valve body (330; 630) being attached to the struts by a plurality of stitches, wherein the plurality of struts include longitudinal struts having first and second ends (532, 534) and which extend from a first end toward a second end of the stent and which terminate at a transition from the non-foreshortening portion to the foreshortening portion, wherein the longitudinal struts are not substantially expandable in the longitudinal direction and are provided in the non-foreshortening portion; wherein at least one of the plurality of stitches is a loose stitch configured to slide longitudinally over a corresponding longitudinal strut when the stent is radially compacted or expanded. a valve body (330; 630) comprising an outer layer and an inner layer; the outer layer being tubular and having a longitudinal axis, an upstream end and a downstream end, the inner and outer layers formed from a thin, flexible material, wherein the thin, flexible layer is not substantially longitudinally stretchable; the inner layer being generally tubular, having a longitudinal axis generally collinear with the outer layer, and being positioned within the tubular outer layer, the inner layer formed from said thin, flexible material and defining a plurality of leaflets adapted to move between an open state and a coapted state, each leaflet having a side edge and a downstream portion, adjacent leaflets of the inner layer being connected by a commissural portion (360, 361; 660, 661); wherein the leaflets are attached to the outer layer along the leaflet side edges, and the commissural portions (360, 361; 660, 661) are attached to the outer layer downstream of at least a portion of the leaflet side edges; and an elongate stent that can be radially compacted to a compacted state and radially expanded to an expanded state, the stent made up of a plurality of struts and having a longitudinal axis, characterised by the stent having a foreshortening portion and a non-foreshortening portion, the foreshortening portion being configured so that as the stent is radially compacted, the foreshortening portion longitudinally expands, and as the stent is radially expanded, the foreshortening portion longitudinally contracts, the valve body (330; 630) being attached to the struts by a plurality of stitches, wherein the plurality of struts include longitudinal struts having first and second ends (532, 534) and which extend from a first end toward a second end of the stent and which terminate at a transition from the non-foreshortening portion to the foreshortening portion, wherein the longitudinal struts are not substantially expandable in the longitudinal direction and are provided in the non-foreshortening portion; wherein at least one of the plurality of stitches is a loose stitch configured to slide longitudinally over a corresponding longitudinal strut when the stent is radially compacted or expanded.