Abstract: The invention relates to a plate heat exchanger, which comprises a plurality of plates located to the side of each other and consisting each of two sheets facing toward each other, which sheets are formed with longitudinal valleys, which facing toward each other form passages between the sheets when the sheets abut each other. The object of the invention is to provide a plate heat exchanger with straight unobstructed passages in order to reduce the problem of clogging and to facilitate cleaning. Between adjacent passages there must be free flow so that washing can be carried out even when a single passage should have been clogged. A further advantage is that the sheets can be formed in press tools without risk of fracture indications to arise. The invention implies that the valleys (5) are formed with grooves (19) transverse to the longitudinal direction of the valley and extending continuously from one outermost located valley to the other outermost located valley.