A heat exchanger is provided that includes plate pairs stacked one above the other. A first flow chamber is formed between the two plates of a plate pair by conducting a first fluid therethrough, a second flow chamber for conducting a second fluid therethrough, wherein the second flow chamber is formed between two adjacent plate pairs, an inlet opening for introducing the first fluid, and an outlet opening for discharging the first fluid. The plates have at least one expansion opening, in particular at least one expansion slit, for reducing stress in the plates. The heat exchanger can withstand high thermal and mechanical loads even over a long time period, such as 10 years.