An apparatus for the regional anticoagulation of the blood, usable for reducing the amount of Ca++ ions in the blood which have to receive a treatment in a circuit for the treatment of blood comprising an inlet conduit (1) for the blood collected from the patient, a device for the treatment of the blood (9), an outlet conduit for returning the treated blood to the patient the apparatus is characterized in that it comprises a membrane (60) made of a material selectively permeable to Ca++ ions.
