['Chest tubes are used to clear blood from around the heart and lungs after heart surgery, but they can be obstructed by a blood clot, leading to retained blood syndrome (RBS). We sought to examine the frequency of RBS and associated morbidity, and to determine the influence of a preventative active chest tube clearance (ATC) protocol on these outcomes.', 'A multidisciplinary team developed a simple protocol to institute ATC to preventatively clear chest tubes of clot during the first 24 hours after heart surgery. An extensive educational in-service was performed before universal implementation (phase 1). We retrospectively compared data collected prospectively from 1849 patients before universal implementation (phase 0) with data from 256 patients collected prospectively after universal implementation (phase 2), and then used propensity matching for outcomes assessment.', 'In propensity-matched patients, 19.9% of patients had interventions for RBS (phase 0). After the implementation of ATC (phase 2), the percent of patients with interventions for RBS was reduced to 11.3%, representing a 43% reduction in RBS (P = .0087). These patients had a 33% reduced incidence of postoperative atrial fibrillation from 30% (78 out of 256) in phase 0 to 20% (52 out of 256) in phase 2. (P = .013).'] Does active clearance of chest drainage catheters reduce retained blood?