Heat exchanger having a bottom, a seal and a lid, - wherein the bottom has two receiving grooves (5, 5') spaced parallel, extending in longitudinal direction of the bottom, which are arranged on two opposite sides of the bottom and are designed to receive lateral protrusions of the lid, - wherein each receiving groove (5, 5') has a groove base (7, 7'), - wherein the bottom has at least three passages which are arranged in one plane spaced parallel from one another as well as spaced from the receiving grooves (5, 5') and extend perpendicularly to and between the receiving grooves (5, 5'), - wherein in the plane between two passages is formed an interim region which is arranged parallel spaced from the groove bases (7, 7') of the receiving grooves (5, 5') by a height difference h, - wherein between each interim region and the groove bases (7, 7') extends parallel to the longitudinal direction of the passages in each case one ramp and the ramps are spaced parallel to one another, - wherein the seal has a peripheral sealing cord, wherein - the seal extends in the receiving grooves (5, 5') and with in each case one sealing web across two ramps and an interim region situated between them, - each ramp is rounded at the transition to the receiving groove (5, 5') with a radius R1 and at the transition to the interim region with a radius R2, - the ramps are inclined at between 20° < α < 65° with respect to the interim region, or have an S-shaped course, wherein a turning point W is arranged in the range from 10% to 80% of the height difference h starting from the groove-base (7, 7') of the receiving groove (5, 5), characterised in that at least one of the ramps is formed as a groove which extends parallel to the longitudinal direction of the passages and in which the seal extends in sections, wherein the ratio of the groove filling degree on the part of the seal in the groove of the at least one ramp to the groove filling degree on the part of the seal in the receiving groove (5, 5') in the compressed state of the seal is between 1.0 and 1.4. - wherein the bottom has two receiving grooves (5, 5') spaced parallel, extending in longitudinal direction of the bottom, which are arranged on two opposite sides of the bottom and are designed to receive lateral protrusions of the lid, - wherein each receiving groove (5, 5') has a groove base (7, 7'), - wherein the bottom has at least three passages which are arranged in one plane spaced parallel from one another as well as spaced from the receiving grooves (5, 5') and extend perpendicularly to and between the receiving grooves (5, 5'), - wherein in the plane between two passages is formed an interim region which is arranged parallel spaced from the groove bases (7, 7') of the receiving grooves (5, 5') by a height difference h, - wherein between each interim region and the groove bases (7, 7') extends parallel to the longitudinal direction of the passages in each case one ramp and the ramps are spaced parallel to one another, - wherein the seal has a peripheral sealing cord, - the seal extends in the receiving grooves (5, 5') and with in each case one sealing web across two ramps and an interim region situated between them, - each ramp is rounded at the transition to the receiving groove (5, 5') with a radius R1 and at the transition to the interim region with a radius R2, - the ramps are inclined at between 20° < α < 65° with respect to the interim region, or have an S-shaped course, wherein a turning point W is arranged in the range from 10% to 80% of the height difference h starting from the groove-base (7, 7') of the receiving groove (5, 5),