Abstract: We have designed a simple cardiopulmonary bypass(CPB)system entitled“Smart Circuit”. Smart Circuit is a closed CPB and consists of a centrifugal pump, an oxygenator, an arterial line, a venous drainage line, and an air venting filter(AVF)that is installed in a venous drainage line. The air venting port in the AVF is connected directly to a wall suction. As a result of an experiment using a mock circuit, the AVF had an equivalent performance for air venting both in the circumstance of positive pressure(arterial circuit)and negative pressure(venous circuit). More than 240 mmHg of negative pressure in the wall suction line was necessary, when the AVF achieved to eliminate the entire air volume from the venous circuit. In the clinical application of four cardiac surgery cases, it took up to seven minutes to set up Smart Circuit. Smart Circuit has the possibility to make easy and safe establishment of CPB in patients undergoing cardiac surgery.