A collapsible-expandable tubular stent (29) constructed of shape-memory material which is implantable into a human heart, which comprises proximal and distal rings (71, 73) and at least two spaced apart posts (69) that extend axially between said rings (71, 73), said distal ring (73) comprising a plurality of distal arms (77) which are connected to the distal ring (73) at only one end and which have a free opposite end； said proximal ring (71) comprising a plurality of, which are connected at only one end to the proximal ring (71) and which have a free opposite end, which proximal arms (75) are constructed to swing radially outward at their free ends.
