A plate heat exchanger, which comprises - a plate pack formed of heat exchanger plates (8, 8', 8") having at least two openings and arranged on top of each other, wherein the plate pack comprises a first end and a second end in the length direction of the plate pack, and which plate pack comprises a first support end plate arranged on the first end of the plate pack, a second support end plate arranged on the second end of the plate pack, and flow passages (9a, 9b) for a first heat exchange medium inside the plate pack are formed of the openings of the heat exchange plates (8, 8', 8") arranged on top of each other, - an outer casing surrounding the plate pack, which outer casing comprises a first end plate and a second end plate and a shell connecting said first and second end plates, - inlet connection tube and outlet connection tube for a first heat exchange medium, arranged through an end plate (3a, 3b) of the outer casing and arranged in connection with the flow passages (9a, 9b) of the plate pack, and - inlet connection tube and outlet connection tube for a second heat exchange medium arranged through the outer casing and arranged in connection with the inside of the outer casing, i.e. with the outside of the plate pack, wherein the inlet connection tube of the first heat exchange medium is arranged through the first end plate of the outer casing and in connection with the first support end plate of the plate pack, and characterized in that the plate heat exchanger further comprises an inner tube, which is arranged inside the inlet connection tube of the first heat exchange medium and which elongates at least partly inside the flow passage of the plate pack and comprises openings (13, 13', 13") which form flow channels into the flow channels inside the plate pack, and 1 - 5 of the first flow channels inside the plate pack are closed, seen from the direction of the inlet connection tube of the first heat exchange medium, and the inner tube is attached to the plate pack inside the flow channel of the plate pack by a gasket or an elastic structure arranged around the inner tube. - a plate pack formed of heat exchanger plates (8, 8', 8") having at least two openings and arranged on top of each other, wherein the plate pack comprises a first end and a second end in the length direction of the plate pack, and which plate pack comprises a first support end plate arranged on the first end of the plate pack, a second support end plate arranged on the second end of the plate pack, and flow passages (9a, 9b) for a first heat exchange medium inside the plate pack are formed of the openings of the heat exchange plates (8, 8', 8") arranged on top of each other, - an outer casing surrounding the plate pack, which outer casing comprises a first end plate and a second end plate and a shell connecting said first and second end plates, - inlet connection tube and outlet connection tube for a first heat exchange medium, arranged through an end plate (3a, 3b) of the outer casing and arranged in connection with the flow passages (9a, 9b) of the plate pack, and - inlet connection tube and outlet connection tube for a second heat exchange medium arranged through the outer casing and arranged in connection with the inside of the outer casing, i.e. with the outside of the plate pack,