The invention relates to a device for extracorporeal blood treatment, comprising a blood treatment unit 1 that comprises at least one compartment 4. The invention further relates to a method for determining a hemodynamic parameter during an extracorporeal blood treatment by means of an extracorporeal blood treatment device. In order to determine the hemodynamic parameter, the conveying direction of the blood pump 10 is reversed from a “normal” blood flow to a “reversed” blood flow. In practice, it has been found that reversing the conveying direction of the blood pump for a measurement for determining a hemodynamic parameter carries the risk of blood clots reaching the patient, despite the dialyser holding back blood clots. The blood treatment device comprises an input unit 23 for inputting a time interval which can be specified by the user, taking into account the patient-specific and system-specific factors. The control and evaluation unit 12 of the blood treatment device is configured such that the operation of the blood pump 10 in the operating mode involving a reversed blood flow is only enabled during the time interval input by means of the input unit, the start of the time interval being determined from the point at which the blood treatment starts.