Collapsible prosthetic heart valves

A prosthetic heart valve, comprising:

• a stent having an expanded condition and a collapsed condition, the stent extending in a longitudinal direction between an inflow end and an outflow end and including a plurality of annularly spaced commissure posts, each commissure post including an elongated slot extending in the longitudinal direction;
• a plurality of leaflets mounted within the stent and operative to allow blood flow in a first direction from the inflow end to the outflow end and to substantially block flow in an opposite direction from the outflow end to the inflow end;
• a sheet material disposed on an inner surface of the stent;
• each of the leaflets having a first end portion, a second end portion, a secured line portion between the first end portion and the second end portion, the secured line portion being attached to the stent and/or to the sheet material, and a free edge between the first end portion and the second end portion and spaced apart from the secured line portion, the free edge being adapted to coapt with the free edge of other ones of the leaflets,
• wherein the first end portion of a first leaflet and the first end portion of a second leaflet adjacent to the first leaflet extend through the elongated slot of one of the commissure posts from an interior of the stent to an exterior of the stent such that the first leaflet and the second leaflet are secured to the one commissure post with at least a part of the first end portions positioned on an outside surface of the stent.