Apparatus for measuring transpulmonary dilution in the coronary circulatory system of a dialysis patient comprises a venous connecting piece (2) with a hemodialyzer outlet connector (13) and a bolus injection port (16), an arterial connecting piece (1) with a hemodialyzer inlet connector (12) and a temperature sensor (30), and an analyzer (21) that has an input channel (47) for the temperature sensor signal and input channels (48, 49) and/or an input device for inputting bolus injection characteristics and is programmed to generate a transpulmonary dilution measurement by determining hemodynamic parameters from the temperature sensor signal and the bolus injection characteristics.
