A heat exchanger including a sealed housing and a body positioned inside the housing, the body including a stack of least one first assembly of first and second plates pressed against each other, between which flows a first fluid, and at least one second assembly of third and fourth plates pressed against each other, between which flows a second fluid, the first and second assemblies being arranged so that they transfer heat between the first and second fluids. This configuration limits the risk of leaks and mixing of the two fluids.