Lung injury was one of the most complications after extracorporeal circulation. As a result of blood exposure to the surface of the extracorporeal circulation circuit, the complements and leukocytes were activated. The activated neutrophil adhered to endothelial cells and released many inflammatory mediators, as protease, oxygen free radicals, arachidonic acid metabolites. All of these inflammatory mediators caused lung injury. In vivo and in vitro, many studies demonstrated that leukocyte depletion in extracorporeal circulation of heart operation could reduce lung injury and improve lung function. Leukocyte depletion could reduce pulmonary resistance, particularly effective in patients with a low preoperative oxygenation capacity and in those for whom an extended period of extracorporeal circulation was required.