In a single needle extracorporeal blood treatment apparatus, an ultrafiltration pump (10) performs a pure ultrafiltration of ultrafiltrate from an hemofilter (4). The blood may be continuously circulated through the hemofilter using a first pump (5), which alternates an higher flow rate during the arterial phase and a lower flow rate during the venous phase, and a second pump (6) which is maintained at a flow rate intermediate between said higher and lower flow rate. The apparatus may be used for treatment of Congestive Heart Failure.