A heat exchanger comprises a plurality of plates (30a, 30b, 32, 34) fixed to each other to form first chambers (36) and second chambers (38), the first chambers being hydraulically connected to each other to form a primary circuit (40) and the second chambers (38) being hydraulically connected to each other to form a secondary circuit (42), hydraulically separated from the primary circuit; the heat exchanger further comprises at least two ports (44 and 46) for the inlet and outlet of a fluid from the primary circuit and at least two ports (48 and 50) for the outlet and inlet of a fluid from the secondary circuit, wherein said ports are arranged along an approximately straight line.