An implantable prosthetic heart valve (10; 310; 600) that is collapsible to a collapsed configuration and expandable to an expanded configuration, the valve (10; 310; 600) comprising: a balloon-expandable annular frame (12; 50; 312) having an inflow end portion (174; 508; 610) and an outflow end portion (506; 612) and being formed from a plastically-expandable material including one or more of: stainless steel or a polymer or a nickel-cobalt-chromium alloy or combinations thereof, and a leaflet structure (14; 204; 314) positioned within the frame (12; 50; 312), wherein the frame (12; 50; 312) comprises: an inflow row of openings at the inflow end portion (174; 508; 610), an outflow row of openings at the outflow end portion (506; 612), and at least one intermediate row of openings between the inflow row of openings and the outflow row of openings, wherein the openings of the inflow row of openings are larger than the openings of the at least one intermediate row of openings, wherein the openings of the outflow row are larger than the openings of the inflow row and the openings of the at least one intermediate row; and wherein the outflow row of openings is formed by a first row of angled struts and a second row of angled struts, connected to one another by a plurality of axially extending window frame portions and a plurality of axially extending struts, said each of the plurality of axially extending window frame portions configured to mount a respective commissure of the leaflet structure (14; 204; 314); wherein each one of the plurality of axially extending window frame portions and each one of the plurality of axially extending struts extends from a first location defined by a convergence of two lower ends of two angled struts of the first row of angled struts to a second location defined by the convergence of two upper ends of two angled struts of the second row of angled struts. a balloon-expandable annular frame (12; 50; 312) having an inflow end portion (174; 508; 610) and an outflow end portion (506; 612) and being formed from a plastically-expandable material including one or more of: stainless steel or a polymer or a nickel-cobalt-chromium alloy or combinations thereof, and a leaflet structure (14; 204; 314) positioned within the frame (12; 50; 312), wherein the frame (12; 50; 312) comprises: an inflow row of openings at the inflow end portion (174; 508; 610), an outflow row of openings at the outflow end portion (506; 612), and at least one intermediate row of openings between the inflow row of openings and the outflow row of openings, wherein the openings of the inflow row of openings are larger than the openings of the at least one intermediate row of openings, wherein the openings of the outflow row are larger than the openings of the inflow row and the openings of the at least one intermediate row; and wherein the outflow row of openings is formed by a first row of angled struts and a second row of angled struts, connected to one another by a plurality of axially extending window frame portions and a plurality of axially extending struts, said each of the plurality of axially extending window frame portions configured to mount a respective commissure of the leaflet structure (14; 204; 314); wherein each one of the plurality of axially extending window frame portions and each one of the plurality of axially extending struts extends from a first location defined by a convergence of two lower ends of two angled struts of the first row of angled struts to a second location defined by the convergence of two upper ends of two angled struts of the second row of angled struts. an inflow row of openings at the inflow end portion (174; 508; 610), an outflow row of openings at the outflow end portion (506; 612), and at least one intermediate row of openings between the inflow row of openings and the outflow row of openings, wherein the openings of the inflow row of openings are larger than the openings of the at least one intermediate row of openings, wherein the openings of the outflow row are larger than the openings of the inflow row and the openings of the at least one intermediate row; and wherein the outflow row of openings is formed by a first row of angled struts and a second row of angled struts, connected to one another by a plurality of axially extending window frame portions and a plurality of axially extending struts, said each of the plurality of axially extending window frame portions configured to mount a respective commissure of the leaflet structure (14; 204; 314); wherein each one of the plurality of axially extending window frame portions and each one of the plurality of axially extending struts extends from a first location defined by a convergence of two lower ends of two angled struts of the first row of angled struts to a second location defined by the convergence of two upper ends of two angled struts of the second row of angled struts.