Heat exchange inefficiencies found in round tube plate fin heat exchangers are eliminated in an aluminum heat exchanger that includes first and second headers (20), (22) and at least one flattened tube (24), (70) extending between the headers (20), (22). A plurality of generally parallel tube runs are defined and each has opposite edges. A plurality of plate fins (26), (50) are arranged in a stack and each has a plurality of open ended slots (34), one for each run of the tubes (24), (70). Each of the tube runs (24), (70) is nested within corresponding slots (26) and the fins (26), (50) with one of the edges (40) of the tube runs extending outwardly of the corresponding fin (34). The assembly is brazed together.