Interface device between a hemodialysis machine and at least one venous tube intended to be connected to a patient's circulatory system for transferring blood from the hemodialysis machine to the circulatory system, this interface device comprising: - a first port adapted to be connected to an output port of the hemodialysis machine; - a venous port to inject blood into the venous tube; the interface device being adapted to selectively adopt a first configuration (A1B1; Etp1) in which the passage of blood between the first port and the venous port is prohibited and a second configuration (A4B2; Etp4) in which the first port is connected to the venous port to allow blood to pass from the first port to the venous port, the interface device being also adapted to form an interface between the hemodialysis machine and an arterial tube for connection to said patient's circulatory system to transfer blood from the circulatory system to the hemodialysis machine, said interface device also comprising: - a second port adapted to be connected to an input port of the hemodialysis machine; - an arterial port for receiving blood from the patient via the arterial tube, the interface device being further adapted to prohibit the passage of blood between the second port and the arterial port when the device is in its first configuration (A1B1; Etp1) and to allow the passage of blood between the second port and the arterial port when the device is in its second configuration (A4B2; Etp4), characterized the interface device comprises a third port (Pblx), the interface device being adapted to selectively adopt an unlocking configuration (A3B2; Etp3a) distinct from said first and second configurations (A1B1, A4B2; Etp1; Etp4), in this unlocking configuration (A3B2) the third port (Pblx) being connected to only one of said venous port or arterial port while the first port and the second port are respectively isolated from the venous port and the arterial port, these venous and arterial ports also being isolated from each other. - a first port adapted to be connected to an output port of the hemodialysis machine; - a venous port to inject blood into the venous tube; the interface device being adapted to selectively adopt a first configuration (A1B1; Etp1) in which the passage of blood between the first port and the venous port is prohibited and a second configuration (A4B2; Etp4) in which the first port is connected to the venous port to allow blood to pass from the first port to the venous port, the interface device being also adapted to form an interface between the hemodialysis machine and an arterial tube for connection to said patient's circulatory system to transfer blood from the circulatory system to the hemodialysis machine, said interface device also comprising: - a second port adapted to be connected to an input port of the hemodialysis machine; - an arterial port for receiving blood from the patient via the arterial tube, the interface device being further adapted to prohibit the passage of blood between the second port and the arterial port when the device is in its first configuration (A1B1; Etp1) and to allow the passage of blood between the second port and the arterial port when the device is in its second configuration (A4B2; Etp4), characterized the interface device comprises a third port (Pblx), the interface device being adapted to selectively adopt an unlocking configuration (A3B2; Etp3a) distinct from said first and second configurations (A1B1, A4B2; Etp1; Etp4), in this unlocking configuration (A3B2) the third port (Pblx) being connected to only one of said venous port or arterial port while the first port and the second port are respectively isolated from the venous port and the arterial port, these venous and arterial ports also being isolated from each other. - a second port adapted to be connected to an input port of the hemodialysis machine; - an arterial port for receiving blood from the patient via the arterial tube, the interface device being further adapted to prohibit the passage of blood between the second port and the arterial port when the device is in its first configuration (A1B1; Etp1) and to allow the passage of blood between the second port and the arterial port when the device is in its second configuration (A4B2; Etp4), characterized the interface device comprises a third port (Pblx), the interface device being adapted to selectively adopt an unlocking configuration (A3B2; Etp3a) distinct from said first and second configurations (A1B1, A4B2; Etp1; Etp4), in this unlocking configuration (A3B2) the third port (Pblx) being connected to only one of said venous port or arterial port while the first port and the second port are respectively isolated from the venous port and the arterial port, these venous and arterial ports also being isolated from each other.