An intravascular blood pump having a rotatable shaft (25) carrying an impeller (34) and a housing (20) with an opening (35) through which the shaft extends with the impeller positioned outside the housing. The shaft and the housing have surfaces (25A, 33A) forming a circumferential gap which has a gap width of no more than 2 µm over the length of the gap and at least one of the surfaces forming the gap is made of a material having a thermal conductivity of at least 100 W/mK, in particular a ceramic material such as SiC.
