Objective:To investigate the mechanism of lung injury after cardiopulmonary resuscitation(CPR) in rats. Methods: Cardiac arrest was induced by asphyxiation(succinylcholine) and ice-cold 0.5 mol/L KCl in rats and CPR was carried out 5 min after arrest. Sixteen adult male Sprague-Dawley rats were randomly allocated into 2 groups:control group(n=8) and CPR group(n=8). The blood gas analysis,serum level of tumor necrosis factor ?(TNF-?),lung tissue wet mass/dry mass ratio(W/D),lung malondialde-hyde(MDA) content and myeloperoxidase(MPO) activities were measured 3 h after CPR. The histological appearances of the lungs were observed under light and electron microscope. Results: Compared to the control group,the lung W/D,serum TNF-?,pulmonary MDA and MPO activity increased dramatically in CPR group while PaO 2 decreased 3 h after resuscitation(P