An implantable prosthetic heart valve configured to be radially collapsible to a collapsed or crimped state for introduction into the body on a balloon delivery catheter and radially expandable using a balloon of the balloon delivery catheter to an expanded state for implanting the prosthetic heart valve at a native aortic valve, the prosthetic heart valve comprising: a radially collapsible and expandable annular frame, the frame having a plurality of angularly spaced commissure attachment posts, wherein the frame further comprises a plurality of axial struts and a plurality of rows of circumferential struts (20, 22, 24) extending between and interconnecting the axial struts, each row of circumferential struts being arranged in a zig-zag pattern extending around a circumference of the frame; an annular skirt member positioned inside of and secured to the frame, wherein the annular skirt member is disposed between the annular frame and a leaflet structure comprising a plurality of leaflets, wherein the annular skirt member has an outflow edge and an inflow edge, wherein the annular skirt member is secured to one of the plurality of rows of circumferential struts (20; 22; 24) of the frame along the outflow edge with sutures, the outflow edge of the annular skirt member having an undulated shape that follows the shape of the row of circumferential struts (20; 22; 24); and wherein the leaflet structure has a scalloped inflow edge portion sutured to an inner surface of the skirt member along a scalloped suture line, each leaflet having an outflow edge, a curved inflow edge and two side flaps extending between respective ends of the outflow edge and the inflow edge, wherein each side flap is secured to an adjacent side flap of another leaflet to form commissures of the leaflet structure, each commissure being attached to one of the commissure attachment posts. a radially collapsible and expandable annular frame, the frame having a plurality of angularly spaced commissure attachment posts, wherein the frame further comprises a plurality of axial struts and a plurality of rows of circumferential struts (20, 22, 24) extending between and interconnecting the axial struts, each row of circumferential struts being arranged in a zig-zag pattern extending around a circumference of the frame; an annular skirt member positioned inside of and secured to the frame, wherein the annular skirt member is disposed between the annular frame and a leaflet structure comprising a plurality of leaflets, wherein the annular skirt member has an outflow edge and an inflow edge, wherein the annular skirt member is secured to one of the plurality of rows of circumferential struts (20; 22; 24) of the frame along the outflow edge with sutures, the outflow edge of the annular skirt member having an undulated shape that follows the shape of the row of circumferential struts (20; 22; 24); and wherein the leaflet structure has a scalloped inflow edge portion sutured to an inner surface of the skirt member along a scalloped suture line, each leaflet having an outflow edge, a curved inflow edge and two side flaps extending between respective ends of the outflow edge and the inflow edge, wherein each side flap is secured to an adjacent side flap of another leaflet to form commissures of the leaflet structure, each commissure being attached to one of the commissure attachment posts.