The invention relates to an apparatus for extracorporeal blood treatment, comprising a blood treatment unit 1 that comprises at least one compartment 3. The invention further relates to an apparatus 15A, 15B for collecting blood clots for a blood line 5, 7 for supplying blood to or removing blood from a blood treatment unit 1 of an extracorporeal blood treatment apparatus, and to a method for determining a hemodynamic parameter during extracorporeal blood treatment using an extracorporeal blood treatment apparatus. 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. It has been found in practice that, in the event of a reversal in the conveying direction of the blood pump in order to carry out a measurement for determining a hemodynamic parameter, there is a risk of blood clots reaching the patients, although the dialyser traps blood clots. The apparatus according to the invention provides an apparatus 15A for catching blood clots, at least in the blood line of the extracorporeal blood circuit I that leads to the blood treatment unit 1 during a “normal blood flow”. The blood treatment unit traps blood clots during blood treatment having a “normal” blood flow. In the case of a “reversed” blood flow, the apparatus for catching blood clots in the blood line that leads to the blood treatment unit 1 during a “normal blood flow” traps blood clots that may have previously accumulated at the inlet of the blood treatment unit.