Abstract: A plate heat exchanger comprising aligned flat heat transfer plates and patterned profiled turbulence plates interposed as spacers between the heat transfer plates. All plates have openings or ports at each of the four corners, some of which are sealed at their periphery so as to direct fluid flow through the flow slits between the heat transfer plates. The gasket seals are part of the turbulence plates and are secured thereto by interlocking corrugations, grooves or keys.