Abstract: An apparatus for extracorporeal oxygenation of a patient's blood during cardiopulmonary bypass surgery. The apparatus comprises a bubble sensor, arranged at or connected to a venous line, for detecting bubbles in the venous blood received from the patient. When air bubbles are detected, a second pump is activated to draw air from an air chamber provided in an air filter connected to the venous line and arranged downstream of the bubble sensor. A first pump draws the blood from the air filter and supplies the blood to an oxygenator and to the patient via an arterial line.