The invention relates to a device for reversing the blood flow for an extracorporeal blood treatment device, comprising an extracorporeal blood circuit (I), which includes an arterial blood line (108A) leading from a patient to a blood treatment unit (204) and a venous blood line (106A) leading from the blood treatment unit to the patient. Furthermore, the invention relates to an extracorporeal blood treatment device with a device for reversing the blood flow, and to a method for determining the reversal of the blood flow during an extracorporeal blood treatment. The device for reversing the blood flow for an extracorporeal blood treatment device according to the invention comprises two valve bodies (102, 104) which are rotated relative to one another for reversing the blood flow. The device for reversing the blood flow according to the invention is characterized by a communication device (210) for receiving an electromagnetic high-frequency field from a read unit (270) of the extracorporeal blood treatment device and for generating at least one identifier characterizing the position of the valve bodies which can be read by the read device.