The invention relates to a heat exchanger, preferably for motor vehicles, comprising a heat exchanger body (11), a first fluid channel (18), which is flowed through by a first fluid (12), and a second fluid channel (36), which is flowed through by a second fluid (14), wherein one of the fluids, either the first fluid (12) or the second fluid (14) is warmer than the other of the fluids, the first fluid (12) or the second fluid (14), wherein, after entering a heat exchanging region, a heat transfer (30) from the warmer fluid (14) to the colder fluid (12) takes place in the heat exchanging region, wherein the first channel (18) and the second fluid channel (36) have in the heat exchanging region at least two shared co-current regions (25) and a shared counter-current region (27) arranged between the co-current regions (25), or have at least two shared counter-current regions (27) and a shared co-current region (25, 125, 225) arranged between the counter-current regions (27).