Abstract: In a heat exchanger comprising a plurality of plates arranged adjacent to each other and defining between them passages for heat exchanging fluids, the plates are provided at their corner portions with openings, the fluids being conveyed to and from the passages via said openings. The openings for one of the fluids are located at one side of the plates and the openings for the other fluid are located at the other side of the plates. The plates are provided with a corrugation pattern which varies in a direction transverse to the flow direction in such way that the passages are narrower shallower at the side of the plates at which the inlet and outlet openings of the respective passages are provided and wider deeper at the opposite side.