In a plate heat exchanger in which the flow rates of the two heat exchanging fluids are different, it is possible to obtain an adjustment to differing proportions of the fluid flows, the pressure drops being given. To this end, the heat exchanger is provided with at least two sections of heat exchanging passages, in at least one of said sections the passages for the two respective fluids having essentially different flow resistances. Furthermore, the proportion of the flow resistances of the passages for the respective fluids in one section differs essentially from the corresponding proportion in at least one other section.