Abstract: Disclosed is a heat exchanger, comprising a tube sheet comprised of plastic and having at least one opening for passage of a heat exchange fluid; and a heat exchanger tube sealed against the tube sheet at the opening, wherein the tube sheet includes in the region of each of the openings a sleeve-like connection nozzle in which an annular groove is defined by inner and outer parts of said nozzle. The groove extends coaxially to the opening and is open toward the heat exchanger tube and the end of the heat exchanger tube is pressed into the groove. The sleeve-like connection nozzles have a middle section (B), which is located in the plane of the tube sheet, and end sections, (A, C) which project on either side of the tube sheet.