Abstract: The invention relates to a heat exchanger (1) of crossflow type for heat exchange between different media, which heat exchanger (1) comprises a plate stack (2) of heat transfer plates for first and second plate types (3, 4). The plate types (3,4) are stacked 5 alternately on one another in the plate stack (2). Each plate type (3, 4) has a side A and a side B with a heat exchange surface (9). The heat exchange surface (9) comprises a pattern (10a, b). In the plate stack (2), adjacent plate types (3, 4) form both first throughflow ducts (14) and second throughflow ducts (15). Said first throughflow ducts (14) have a larger volume than said second throughflow ducts (15), the volume of a first medium (16) in said 10 first throughflow ducts (14) being greater than the volume of a second medium (17) in said second throughflow ducts (15).