Extracorporeal blood treatment device comprising: an extracorporeal circuit comprising an arterial section and a venous section, a dialyzer and a dialyzing liquid circuit, wherein the extracorporeal circuit and the dialyzing liquid circuit are separated from each other by a membrane provided in the dialyzer; in the venous section a first sensor is provided, which is configured to acquire a hematocrit percentage in a liquid flowing through the venous section; in the arterial section a second sensor (24, 48) is provided, which is configured to acquire a hematocrit percentage in a liquid flowing through the arterial section; and the extracorporeal blood treatment device further comprises a control unit which is configured to control a reinfusion of blood such that a dialyzing liquid is supplied from the dialyzing liquid circuit via the membrane of the dialyzer to the extracorporeal circuit, which during the reinfusion displaces the blood present in the extracorporeal circuit towards a patient to return the blood to the patient via both the venous section and the arterial section, characterized in that the control unit is configured to discontinue the reinfusion via the venous section if it is acquired by the first sensor or calculated or predicted by the control unit on the basis of information acquired by the first sensor that the hematocrit percentage falls below a predetermined limit value, and to discontinue the reinfusion via the arterial section if it is acquired by the second sensor (24, 48) or calculated or predicted by the control unit on the basis of information acquired by the second sensor (24, 48) that the hematocrit percentage falls below the predetermined limit value. an extracorporeal circuit comprising an arterial section and a venous section, a dialyzer and a dialyzing liquid circuit, wherein the extracorporeal circuit and the dialyzing liquid circuit are separated from each other by a membrane provided in the dialyzer; in the venous section a first sensor is provided, which is configured to acquire a hematocrit percentage in a liquid flowing through the venous section; in the arterial section a second sensor (24, 48) is provided, which is configured to acquire a hematocrit percentage in a liquid flowing through the arterial section; and the extracorporeal blood treatment device further comprises a control unit which is configured to control a reinfusion of blood such that a dialyzing liquid is supplied from the dialyzing liquid circuit via the membrane of the dialyzer to the extracorporeal circuit, which during the reinfusion displaces the blood present in the extracorporeal circuit towards a patient to return the blood to the patient via both the venous section and the arterial section, characterized in that the control unit is configured to discontinue the reinfusion via the venous section if it is acquired by the first sensor or calculated or predicted by the control unit on the basis of information acquired by the first sensor that the hematocrit percentage falls below a predetermined limit value, and to discontinue the reinfusion via the arterial section if it is acquired by the second sensor (24, 48) or calculated or predicted by the control unit on the basis of information acquired by the second sensor (24, 48) that the hematocrit percentage falls below the predetermined limit value.