Abstract: In a plate heat exchanger, in which the plates are provided with a turbulence generating pattern of grooves and ridges which also form supporting points for plates disposed adjacent to each other, the thermal treatment of a medium will be different in different parts of one and the same passage due to the different length of different flow paths within the passage. In order to equalize the differences of thermal treatment within one and the same passage and/or to provide mutually different treatment of the heat exchanging media, each passage is formed by plates corrugated in a pattern which is unsymmetrical with regard to the central plane of the plates, the ridges and grooves of plates disposed adjacent to each other extending in mutually different directions relative to the longitudinal axis of the plates.