A heat exchanger includes a conduit, a header, and a swirler been formed as a unitary piece by additive manufacturing. The swirler is disposed within the conduit and the header and is arranged to disperse a flow from an inlet flow path a heat exchanger matrix. The swirler extends a only portion of the length of the header between the conduit and the heat exchanger matrix and thereby provides space within the header for fluid to diffuse before entering the heat exchanger matrix.