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 , 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 , 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 . <EOS>