After the implantation of a biventricular assist device hemodynamic evaluation is difficult. The device itself frequently does not report the real outflow as it does not take into account the native cardiac output. Other methods used for cardiac output measurements cannot be employed for technical reasons and/or because their measurements could be misleading. The consequences are twofold; firstly, cardiac output cannot be estimated with accuracy. Secondly, the adequacy of oxygen supply and demand cannot be assessed. In order to monitor the adequacy of cardiac output in patient with Berlin heart biventricular support, the authors propose an original non invasive method to measure mixed venous blood saturation.