A heat exchanger (1) consists of a plurality of disks (4) which are assembled to form a heat exchanger block or disk stack (16) and which are formed in each case from sheets (22) joined together in pairs and enclose between them at least one cavity designed as a duct. The cavity is delimited by the insides of the sheets (22). In the duct, an internal fluid flows in the longitudinal direction of the disks (4) and, on the outside of the disks, an external fluid flows transversely to the direction of flow of the internal fluid. Each sheet (22) has elevations (26, 33) out of the disk plane, which are formed by material deformation and are directed both into the inside of the disk and toward the outside of the disk, the elevations (33) directed toward the outside of the disk being configured as elongate stamped-out portions.