A heat exchanger (10) comprises an alternating stacking of first plates (12) and second plates (14) provided respectively with first corrugations (16) separated by a first pitch (P1) and second corrugations (18) separated by a second pitch (P2), which is different from the first pitch (P1). Between the plates, first flow channels are defined having a first cross sectional area adapted to a first fluid (F1) which alternate with second flow channels having a second cross sectional area adapted to a second fluid (F2). The invention applies in particular to heat exchangers for motor vehicles.