A heat exchanger with at least one louver arrangement in the region between associated tubes for the heat transfer from one medium to another medium. The louver arrangement is provided with an inflow part and an outflow part corresponding to the inflow part. Both flow parts each have one outside louver, at least one intermediate louver and one inside louver, whereby the inside louvers are connected to each other and the louvers of one flow part are arranged inclined relative to the louvers of the other flow part and provided with louver geometry elements--length L, width B, angle of inclination .alpha.--, whereby between adjacent inclined louvers each there are passage slots for the flowing medium. The louver arrangement is provided at least in one of both flow parts with at least one at least single-curved intermediate louver and/or at least one multiple-curved outside louver and/or inside as geometry elements.