An apparatus for extracorporeal blood treatment comprising: - a filtration unit having a primary chamber and a secondary chamber separated by a semi-permeable membrane; - a blood circuit comprising at least: • a blood withdrawal line extending between a first end connected to an inlet of the primary chamber and a second end suitable for connection to a patient; and • a blood return line extending between a first end connected to an outlet of the primary chamber and a second end suitable for connection to said patient; - a blood pump operative on the blood circuit; - a fluid circuit comprising at least: • a dialysis fluid effluent line connected to an outlet of the secondary chamber; • a fluid supply source for providing a sterile fluid, such as a dialysis or replacement fluid; - at least one gas inlet to allow gas to enter into the blood circuit; - a control unit configured to perform a blood restitution procedure towards the patient for ending an extracorporeal blood treatment and before disconnecting the patient, said blood restitution procedure comprising the following steps: > infusing a predetermined amount of sterile fluid from the supply source into the blood circuit, said infusing step of sterile fluid defining at least one fluid-blood interface into the blood circuit; > causing a predetermined amount of gas to enter into the blood circuit from the gas inlet to define at least one gas-fluid interface into the blood circuit, wherein at least part of the sterile fluid is interposed between the at least one fluid-blood interface and the at least one gas-fluid interface; > moving simultaneously: o at least part of the extracorporeal blood contained in the blood circuit, o said at least part of the sterile fluid interposed between the fluid-blood interface and the gas-fluid interface, and o at least part of the gas towards the patient to restitute part of the blood to the patient before patient disconnection. - a filtration unit having a primary chamber and a secondary chamber separated by a semi-permeable membrane; - a blood circuit comprising at least: • a blood withdrawal line extending between a first end connected to an inlet of the primary chamber and a second end suitable for connection to a patient; and • a blood return line extending between a first end connected to an outlet of the primary chamber and a second end suitable for connection to said patient; • a blood withdrawal line extending between a first end connected to an inlet of the primary chamber and a second end suitable for connection to a patient; and • a blood return line extending between a first end connected to an outlet of the primary chamber and a second end suitable for connection to said patient; - a blood pump operative on the blood circuit; - a fluid circuit comprising at least: • a dialysis fluid effluent line connected to an outlet of the secondary chamber; • a fluid supply source for providing a sterile fluid, such as a dialysis or replacement fluid; • a dialysis fluid effluent line connected to an outlet of the secondary chamber; • a fluid supply source for providing a sterile fluid, such as a dialysis or replacement fluid; - at least one gas inlet to allow gas to enter into the blood circuit; - a control unit configured to perform a blood restitution procedure towards the patient for ending an extracorporeal blood treatment and before disconnecting the patient, said blood restitution procedure comprising the following steps: > infusing a predetermined amount of sterile fluid from the supply source into the blood circuit, said infusing step of sterile fluid defining at least one fluid-blood interface into the blood circuit; > causing a predetermined amount of gas to enter into the blood circuit from the gas inlet to define at least one gas-fluid interface into the blood circuit, wherein at least part of the sterile fluid is interposed between the at least one fluid-blood interface and the at least one gas-fluid interface; > moving simultaneously: o at least part of the extracorporeal blood contained in the blood circuit, o said at least part of the sterile fluid interposed between the fluid-blood interface and the gas-fluid interface, and o at least part of the gas > infusing a predetermined amount of sterile fluid from the supply source into the blood circuit, said infusing step of sterile fluid defining at least one fluid-blood interface into the blood circuit; > causing a predetermined amount of gas to enter into the blood circuit from the gas inlet to define at least one gas-fluid interface into the blood circuit, wherein at least part of the sterile fluid is interposed between the at least one fluid-blood interface and the at least one gas-fluid interface; > moving simultaneously: o at least part of the extracorporeal blood contained in the blood circuit, o said at least part of the sterile fluid interposed between the fluid-blood interface and the gas-fluid interface, and o at least part of the gas o at least part of the extracorporeal blood contained in the blood circuit, o said at least part of the sterile fluid interposed between the fluid-blood interface and the gas-fluid interface, and o at least part of the gas