Apparatus for use with a delivery catheter, the apparatus comprising an endovascular stent-graft, which is configured to initially be positioned in the delivery catheter in a radially-compressed state, and to assume a radially-expanded state upon being deployed from the delivery catheter, and which comprises: a structural member, which comprises a plurality of structural stent elements, at least a portion of which structural stent elements define a stent body when the stent-graft assumes the radially-expanded state; and a fluid flow guide, which comprises at least one biologically-compatible substantially fluid-impervious flexible sheet, and which is coupled to the stent body, wherein, when the stent-graft assumes the radially-expanded state, the fluid flow guide is shaped so as to define radially-diverging and radially-converging portions (13, 19), which together define a bulge that extends radially outward, which bulge has a greatest cross-sectional area that is equal to at least 120% of a cross-sectional area of a narrowest portion of the stent-graft rostral to the bulge, characterized in that when the stent-graft assumes the radially-expanded state: a first subset of the structural stent elements of the stent body are configured to cause the fluid flow guide to define the bulge, a second subset of the structural stent elements of the stent body are not configured to cause the fluid flow guide to define the bulge, and the structural stent elements of the first subset at least partially overlap the structural stent elements of the second subset lengthwise along the stent body. a structural member, which comprises a plurality of structural stent elements, at least a portion of which structural stent elements define a stent body when the stent-graft assumes the radially-expanded state; and a fluid flow guide, which comprises at least one biologically-compatible substantially fluid-impervious flexible sheet, and which is coupled to the stent body, wherein, when the stent-graft assumes the radially-expanded state, the fluid flow guide is shaped so as to define radially-diverging and radially-converging portions (13, 19), which together define a bulge that extends radially outward, which bulge has a greatest cross-sectional area that is equal to at least 120% of a cross-sectional area of a narrowest portion of the stent-graft rostral to the bulge, characterized in that when the stent-graft assumes the radially-expanded state: a first subset of the structural stent elements of the stent body are configured to cause the fluid flow guide to define the bulge, a second subset of the structural stent elements of the stent body are not configured to cause the fluid flow guide to define the bulge, and the structural stent elements of the first subset at least partially overlap the structural stent elements of the second subset lengthwise along the stent body. a first subset of the structural stent elements of the stent body are configured to cause the fluid flow guide to define the bulge, a second subset of the structural stent elements of the stent body are not configured to cause the fluid flow guide to define the bulge, and the structural stent elements of the first subset at least partially overlap the structural stent elements of the second subset lengthwise along the stent body.