A collapsible stent for an implantable prosthetic valve incorporates leaflet-supporting members having relatively large surface area in comparison to other members defining the remainder of the stent. The leaflet-supporting members may have openings extending through them. The valve leaflets may be attached to the stent so that an attached edge of each leaflet extends along the leaflet-supporting members and is attached to the members by polymer integral with the leaflet overlying the leaflet supporting members and extending into the openings of the leaflet supporting members. The secure attachment resists stress on the leaflets.