Method and apparatus for ultrafiltration of a patient being overhydrated due to congestive heart failure, comprising a cassette (25) having four inlets/outlets (25a, 25b, 25c, 25d). A patient tube (22) is connected to a patient connector (21), intended to be connected to a patient line (3) for access to a peritoneal cavity (2) of the patient (1). The patient tube comprises a flow pump (15) for addition and removal of a peritoneal fluid between the cassette (25) and the peritoneal cavity (2). The fluid is introduced into an intermittent bag (33) controlled by an intermittent valve (18) and then returned the same way back to the peritoneal cavity. Glucose is metered into the fluid entering the peritoneal cavity by means of a glucose pump (15). Glucose is replenished continuously or intermittently for keeping a concentration of the osmotic agent substantially constant in the peritoneal cavity. After treatment, the peritoneal fluid is drained to a drain bag (30), wherein the drain tube (31) comprises a drain valve (17) and an albumin filter.
