The invention relates to a device for transanally introducing an infusion into the rectum or colon of a patient, said device comprising a catheter with a catheter shaft and an inflatable balloon, comprising a distal terminal balloon section of larger radius and generally spherical or discoid shape, and, disposed proximal to this distal terminal balloon section, a tapered balloon section having a reduced radius, the tapered balloon section of the device being adapted to be placed transanally, such that the enlarged distal terminal balloon section is placed intrarectally wherein the balloon is fixed onto the catheter shaft only at fixation points located at the ends of the balloon, wherein both balloon ends taper approximately to a shaft dimension of the catheter shaft supporting the balloon； according to the present invention, the difference between the larger radius of the distal terminal balloon section and the reduced radius of the proximally adjacent, tapered balloon section is either in the pressurized state of the balloon at 30 mbar, smaller than the difference between the larger radius of the distal terminal balloon section and the reduced radius of the proximally adjacent, tapered balloon section in the pressurized state of the balloon at 100 mbar, or is in the inflated, but unpressurized state of the balloon greater than the distance between the distal end of the catheter shaft on the one hand and the distal fixation point of the balloon to the catheter shaft on the other hand.
