Occlusion of chest drainage tubes by thrombus is not uncommon after open heart operations. It has been suggested that by coating the tube with phosphatidylcholine (PC), the most prominent phospholipid in the erythrocytes outer membrane, it may be possible to overcome the blood-material interaction responsible for thrombus formation. To test this hypothesis 102 patients (75 males; mean age, 57 +/- 10 years) were randomly allocated to receive either PC-coated or noncoated 32F chest drainage tubes. Preoperative status, type and length of operation, and duration of drainage were similar in the two groups as was postoperative blood loss. Patients receiving PC-coated tubes, however, had less residual blood clot in the tube after removal (0.7 +/- 0.1 versus 3.1 +/- 0.3 g; p < 0.001), a reduced incidence of pericardial effusions (17.6% versus 41.2%; p < 0.01), fewer postoperative supraventricular arrhythmias (2 of 51 versus 10 of 51; p < 0.002), and a shorter hospital stay (8.4 +/- 0.3 versus 9.7 +/- 0.5 days; p < 0.05). Late cardiac tamponade developed in 2 patients in the noncoated group 6 and 10 days postoperatively, which required reexploration. The data show that PC-coated chest drainage tubes are less susceptible to occlusion by thrombus and their use is associated with a significant reduction in postoperative morbidity.