A heat exchanger may include input-side and output-side tube plates and tubes supported therein, forming a first flow duct for a first medium. A housing may surround the tube plates and the tubes, forming a second flow duct for a second medium running between the tubes in the housing. The heat exchanger may further include at least one turbulence-generating insert arranged in the second flow duct between the tubes, the insert having ducts with permeable side walls for the second medium, and at least one dividing wall duct having closed side walls and being spaced apart at least at one longitudinal end from the housing. The at least one dividing wall duct may be designed to be open at both longitudinal ends, may be produced by a compression process, and may have a rising first flank and a second flank engaging below the second flank.