The ultimate purpose of the research proposal is the design of a modular hybrid system, that could easily convert from form a closed to a semi-closed circuit according to the indication, that could expand the potential of minimal extracorporeal circulation and could ultimately become the new standard circuit in performing every type of cardiac surgery. The term modular refers to an additionally mounted, clamped-off venous reservoir which allows to run the system as an open circuit in case of anticipated volume loss (ie bleeding, complex procedures, long bypass run). This measure follows the proverb 'always expect the unexpected' and offers the clinical practitioner an additional safety margin in case of unexpected intraoperative events. Unique design of this circuit would offer the opportunity of reducing cost, while at the same time improving clinical outcome. Preliminary design of this circuit, performed in our institution, is presented schematically in the appendix. After completion of the study protocol the designed circuit will be patented.