The invention relates to a plate heat exchanger and a method for constructing multiple passes in the plate heat exchanger. A plate heat exchanger (1) according to the invention comprises at least one stopper plate (7) arranged between the outer surface of the plate pack (6) and the shell (2) of the outer casing of the heat exchanger for arranging multiple passes for the second heat exchange medium to the heat exchanger, wherein the stopper plate (7) is welded to an additional planar structure of the plate pack.