The invention refers to a plate heat exchanger comprising a first end plate (1), a second end plate (2) and a number of heat exchanger plates (3), forming first plate interspaces (I) and second plate interspaces (II), in alternating order. The heat exchanger plates comprise a first outermost plate pair (5), a second outermost plate pair (6) and intermediate plate pairs (7). The first end plate and the heat exchanger plates comprise first porthole areas (11, 12) for first porthole channels (13, 14) for the formation of inlet and outlet for a first medium to and from the first plate interspaces, and second porthole areas (21, 22) for the formation of second porthole channels (23, 24) for inlet and outlet for a second medium to and from the second plate interspaces. The first porthole areas of the heat exchanger plates of the second outermost plate pair form portholes and the second porthole areas of these heat exchanger plates are closed.