A combined device having a reservoir for venous blood and a reservoir for cardiotomy blood is disclosed. The device is characterized in that the venous reservoir is separated from the cardiotomy reservoir by a partition which includes a plurality of apertures. The apertures are in fluid communication with a plurality of ducts and passageways which are configured to provide various modes of operation depending upon whether, for the particular surgical conditions, it is desired to mix venous and cardiotomy blood, or to isolate those blood pools from each other.