Abstract: Heat exchanger core comprising flat plate fluid U flows tubes stacked on one another and operatively connected to one another by discrete fluid supply and suction lines. These lines extending through side-by-side tank portions of the tubes to improve structural integrity of the core and respectively have fluid feed and exhaust openings communicating with the tanks and sized to provide even distribution of the heat exchanger fluid to the tubes. With the supply and suction lines, evenly distributing the heat exchanger fluid, tank size and capacity is optimized and the requirement for large capacity deep draw tanks of prior constructions is eliminated.