A plate heat exchanger, the exchanger comprising: - a plurality of plates (3, 11) stacked upon each other, the plates (3, 11) delimiting between them alternately a plurality of primary passages and a plurality of secondary passages, the primary passages being provided for circulation of a primary fluid and the secondary passages being provided for the circulation of a secondary fluid; - a first collector for supplying the secondary passages with secondary fluid and a collector for discharging the secondary fluid into which open the secondary passages; - the plates (3, 11) being parallel to a determined longitudinal axis and having a common middle plane containing the longitudinal axis, characterized in that - the exchanger comprises a second secondary supply collector, the first and second secondary supply collectors (19, 21) and the secondary discharge collector being made in the plates (3, 11) and substantially extending perpendicularly to the plates (3, 11), - the secondary discharge collector is located at a first longitudinal end of the plates (3, 11) in the middle plane, the first and second secondary supply collectors (19, 21) being located at a second longitudinal end of the plates (3, 11) opposite to the first, symmetrically relatively to the middle plane and away from the middle plane, - the exchanger comprises first and second groups of secondary passages fluidically connecting the first and second secondary supply collectors (19, 21) to the secondary discharge collector respectively, the first and second groups of secondary passages each having a first total passage section at half-length between the first and second secondary supply collectors (19, 21) and the secondary discharge collector respectively, the first and second groups of secondary passages each having a second total passage sectionof less than 10% of the first passage section at the output of the first and second secondary supply collectors (19, 21) respectively. - a plurality of plates (3, 11) stacked upon each other, the plates (3, 11) delimiting between them alternately a plurality of primary passages and a plurality of secondary passages, the primary passages being provided for circulation of a primary fluid and the secondary passages being provided for the circulation of a secondary fluid; - a first collector for supplying the secondary passages with secondary fluid and a collector for discharging the secondary fluid into which open the secondary passages; - the plates (3, 11) being parallel to a determined longitudinal axis and having a common middle plane containing the longitudinal axis, - the exchanger comprises a second secondary supply collector, the first and second secondary supply collectors (19, 21) and the secondary discharge collector being made in the plates (3, 11) and substantially extending perpendicularly to the plates (3, 11), - the secondary discharge collector is located at a first longitudinal end of the plates (3, 11) in the middle plane, the first and second secondary supply collectors (19, 21) being located at a second longitudinal end of the plates (3, 11) opposite to the first, symmetrically relatively to the middle plane and away from the middle plane, - the exchanger comprises first and second groups of secondary passages fluidically connecting the first and second secondary supply collectors (19, 21) to the secondary discharge collector respectively, the first and second groups of secondary passages each having a first total passage section at half-length between the first and second secondary supply collectors (19, 21) and the secondary discharge collector respectively, the first and second groups of secondary passages each having a second total passage sectionof less than 10% of the first passage section at the output of the first and second secondary supply collectors (19, 21) respectively.