An apparatus, comprising: a blood pump, comprising: an axial shaft configured for insertion into, and rotation within, a body of a subject; a coupling element, comprising: a first portion, which is disposed around the axial shaft and: is made of a shape-memory material, is shaped to define one or more slits that facilitate a radial expansion of the first portion such that the first portion is placeable around the axial shaft, and is shape-set to have an inner diameter that is smaller than an outer diameter of the axial shaft such that, following a placement of the first portion around the axial shaft, the first portion becomes radially contracted around, and thus locked in place with respect to, the axial shaft; and a second portion; and an impeller, comprising: a bushing (58, 64) coupled to the second portion of the coupling element; and one or more blades coupled to the bushing (58, 64) such that, as the axial shaft rotates, the blades rotate, thereby pumping blood of the subject. an axial shaft configured for insertion into, and rotation within, a body of a subject; a coupling element, comprising: a first portion, which is disposed around the axial shaft and: is made of a shape-memory material, is shaped to define one or more slits that facilitate a radial expansion of the first portion such that the first portion is placeable around the axial shaft, and is shape-set to have an inner diameter that is smaller than an outer diameter of the axial shaft such that, following a placement of the first portion around the axial shaft, the first portion becomes radially contracted around, and thus locked in place with respect to, the axial shaft; and a second portion; and a first portion, which is disposed around the axial shaft and: is made of a shape-memory material, is shaped to define one or more slits that facilitate a radial expansion of the first portion such that the first portion is placeable around the axial shaft, and is shape-set to have an inner diameter that is smaller than an outer diameter of the axial shaft such that, following a placement of the first portion around the axial shaft, the first portion becomes radially contracted around, and thus locked in place with respect to, the axial shaft; and is made of a shape-memory material, is shaped to define one or more slits that facilitate a radial expansion of the first portion such that the first portion is placeable around the axial shaft, and is shape-set to have an inner diameter that is smaller than an outer diameter of the axial shaft such that, following a placement of the first portion around the axial shaft, the first portion becomes radially contracted around, and thus locked in place with respect to, the axial shaft; and a second portion; and an impeller, comprising: a bushing (58, 64) coupled to the second portion of the coupling element; and one or more blades coupled to the bushing (58, 64) such that, as the axial shaft rotates, the blades rotate, thereby pumping blood of the subject. a bushing (58, 64) coupled to the second portion of the coupling element; and one or more blades coupled to the bushing (58, 64) such that, as the axial shaft rotates, the blades rotate, thereby pumping blood of the subject.