A method is disclosed for producing a heat exchanger, in particular for a motor vehicle, a method whereby fluid circulation tubes (3) are inserted into through holes in heat exchange fins (4) and the fluid circulation tubes (3) are subjected to expansion in such a way as to expand a contour (22) of the tubes (3) to ensure contact with the fins (4) at the through holes and, additionally, for at least one of the tubes (3), to deform a concave portion (24) of the contour (22) of the tube or tubes (3), in such a way as to correspondingly deform the through holes. A device for implementing the method and an exchanger obtained by the method are also disclosed.