A control system for controlling a quantity of blood in a blood reservoir (10) of a perfusion system supplied by a venous line (V), wherein a pump (20) circulates blood from the blood reservoir (10) through an outgoing line(A), comprises a venous flow sensor (22) to measure a venous blood flow rate,an outlet flow sensor (24) to measure an outgoing blood flow rate, and a controller to control the pump (20) to prevent the outgoing blood flow rate from exceeding the venous blood flow rate. Thereby,a decrease of blood in the blood reservoir(10) can be arrested.
