A heat exchanger, in particular for cooling the exhaust of a motor vehicle internal combustion engine, is disclosed, the heat exchanger comprising a first partial heat exchanger with at least one first flow channel through which a medium to be cooled is to flow and at least one third flow channel through which a first coolant is to flow, at least one second partial heat exchanger with at least one second flow channel through which a medium to be cooled is to flow and at least one fourth flow channel through which a second coolant is to flow, wherein the at least one first flow channel and the at least one second flow channel are fluidly connected, and the at least one first flow channel and the at least one second flow channel have at least one first specific heat transfer surface and at least one second heat transfer surface, wherein second specific heat transfer surface area, divided by first specific heat transfer surface area, yields a quotient (ψ), the at least one first flow channel having a larger quotient (ψ) than second flow channel.