in a ring 16 which protrudes by means of a tab 16 a from the rigid base 14 for supporting the venous bag 8 of course the means for connecting the cardiotomy reservoir selectively to the venous reservoir and to the venous bag may assume any configuration a tube 17 is also provided which protrudes from the outflow coupling 3 a of the cardiotomy reservoir which is adapted to be connected selectively to the coupling 6 b of the venous reservoir 4 and to the coupling 8 a of the venous bag 8 the tube 17 is adapted to be blocked when there is no need to supply blood from the cardiotomy reservoir by means of the known scissor like tool known as clamp and a tube provided with a tap might be provided in its place the venous reservoir 4 and the venous bag 8 are provided with identical means for monolithic connection to the oxygenation unit 9 which comprise the identical tabs 18 and 19 which protrude respectively from the bottom of the reservoir 4 and from the rigid base 14 for supporting the bag 8 and are adapted to enter a slot 20 provided on the lid.