A device for heat treatment of body tissue, comprising a catheter (12), which is insertable in the body and is equipped with an expandable fluid receptacle (11). The fluid receptacle (11) contains heating means (10) for convective heating of fluid contained in the receptacle (11) and, thus, heating of the tissue in an area of treatment located in the environment surrounding the fluid receptacle (11). The heating device (10) is connected to an energy supply unit (14) located outside of the body.