Abstract: The central venous sensor assembly comprises a catheter body with several proximal ports. The catheter portion placed in the vena cava superior is equipped with a proximal flux measurement unit, and the catheter portion placed in the vena cava inferior is equipped with a distal flux measurement unit. A first input channel supplies a measurement signal indicative of a flux vp to the evaluation unit from which the latter calculates a blood flow in the vena cava superior. Likewise, a second input channel supplies a measurement signal indicative of a flux vd to the evaluation unit from which the latter calculates a blood flow rate in the vena cava inferior. Due to continuity, the sum of the flow rates in the upper and lower central veins corresponds to the flow rate through the right heart and in the pulmonary artery and thus to cardiac output.