The invention relates to a plate heat exchanger, composed of trough-shaped heat exchanger plates which are stacked one in the other and whose edges bear against one another. The plates can have flow ducts, located between the heat exchanger plates for a cooling fluid and for another fluid. The flow ducts are fitted with inserts in the form of turbulator plates. The heat exchanger can include at least four inlet and outlet openings in the corners of the heat exchanger plates which form two vertical ducts for the cooling fluid and two vertical ducts for the other fluid in the stack. The inserts in the flow ducts for the cooling fluid are embodied in one part or a plurality of parts. The flow ducts for the cooling fluid are equipped, in the regions around the openings, with plate-like inserts which have guide ducts with a width, and are provided with the turbulator plate in a central region between the plate-like inserts. The openings can be arranged right in the corners in such a way that only a narrow strip remains, which is occupied by a guide duct which is formed in the plate-like inserts and which has a significantly smaller width than the width of the other guide ducts.