['Standard extracorporeal circulation (ECC) remains the staple procedure for cardiac surgeons. Despite modern membrane oxygenators and arterial filters micro bubbles are regularly detected in the arterial line. We investigated whether initial deairing of the venous drainage during connection can reduce the quantity and size of micro bubbles on the arterial side.', '12 patients underwent isolated coronary artery revascularization with conventional ECC using a two-stage venous catheter and an open, passive venous return into a reservoir. In 6 patients (Control) the venous catheter was routinely connected to the venous line, thereby accepting moderate incorporation of air. In another 6 patients (deaired) the catheter was connected avoiding any visible air entrapment. A bubble counter was used to detect the number and size of any micro bubbles in the arterial line of the ECC. The total number of bubbles as well as the number of bubbles of different sizes was assessed directly after initiation of ECC and during the first 60 sec.', 'All patients had an uneventful surgery with a normal postoperative course. In the Control group a considerable number of bubbles of all sizes occurred initially and after 60 sec. In contrast, very few bubbles were detected in the deaired group.'] Does deairing of the venous drainage in standard extracorporeal circulation result in a profound reduction of arterial micro bubbles?