HEAT EXCHANGER

The invention relates to a heat exchanger, in particular an exhaust gas cooler, with tubes formed in one piece or from two shell-like disks, which form a first and a second fluid channel, wherein the respective fluid channels are arranged adjacent to one another, wherein the first fluid channel is open at at least one of its ends for inlet and/or outlet of the first fluid, wherein the tubes are formed at the ends by a step inward or outward such that the second fluid channels are closed at their ends, wherein the step in the corner regions of the tube has a greater extension T in the tube longitudinal direction than between the corner regions.