A device for reducing or removing stenosis present in a blood vessel by means of a working catheter (7) is described. The working catheter comprises a lumen (8) forming a first working channel (9), extending from the distal end (11) to the proximal end of the working catheter for inserting an instrument (38) to reduce or remove the stenosis. Furthermore, a balloon catheter (16) is provided, which is configured separately from the working catheter, the balloon catheter comprising a sealing balloon (22) in the region of the distal end (21) thereof. The balloon catheter comprises two lumen (18, 20) that are configured separately from each other, of which one is connected to the sealing balloon for the dilation of the same, while the other one forms a second working channel (19) extending from the distal end to the proximal end of the balloon catheter. The sealing balloon is configured for the lateral encompassing of the distal end region of the working catheter such that if a working catheter and a balloon catheter are inserted into the blood vessel next to each other a seal is formed between the outsides of the working catheter and of the balloon catheter and the inside wall of the blood vessel by means of the dilated sealing balloon.
