A plate heat exchanger comprising a plurality of plates (12,13) which are stacked against each other and which are of a first and second type in order to form flow channels for a first and second medium. The plates form a heat exchanger block (2) with an upper side and a lower side and with two opposite side surfaces (10) and front faces (9). The first flow channels are peripherally sealed for the first medium and are fluidically connected to distributor and collector channels which are arranged in a vertical position with respect to the plate plane and which lead into inlet and outlet connection pieces (6,7) which are respectively arranged on the upper side and/or lower side (3,11). The second flow channels are open at the front surfaces (9) thereof and are sealed at the side surfaces (10) thereof. The open sides (9) form an inlet and outlet plane for the second medium.