The present invention provides a heat exchanger including a stack of plates which form ducts. Each of the plates can have at least two openings which, in the plate stack, form at least one collecting duct and one distributor duct which connect the ducts in terms of flow. A base plate can be arranged on the plate stack and can have a seal for sealing off the heat exchanger and a flow deflector for manipulating flow through the heat exchanger. The seal and the flow deflector can form a common component.