In this study, 30 patients undergoing elective myocardial revascularization were divided randomly in three groups (10 patients each) with different management of the lungs during CPB: Group 1, lungs deflated; Group 2, static inflation with PEEP = 5 cmH2O and FIO2 = 1.0; Group 3, static inflation with PEEP = 5 cmH2O and FIO2 = 0.21. Measurements (Qs/Qt, P(A-a)O2, PaO2, Cstat, Cdyn, PIP, AUTO-PEEP, Rrs,max, Rrs,min and DRrs) were performed after the induction of anesthesia (T0), 20 minutes (T1) and 2 hours (T2) after the end of CPB. Respiratory mechanics data were obtained only at T0 and T2 because the sternal retraction. The Group 1 presented a statistically significant increase in Qs/Qt, P(A-a)O2 and Peak Inspiratory Pressure (PIP); in this group we noticed also a decrease in PaO2 values, static compliance (Cstat) and dynamic compliance (Cdyn) values comparing basal versus T1 and T2 values. The Group 2 showed a statistically significant increase in Qs/Qt and P(A-a)O2 values; also in this group we observed a statistically significant decrease in PaO2 and Cdyn values comparing basal versus T1 and T2 values. The Group 3 presented a statistically significant decrease in PaO2 values (basal versus T1 and T2); this group also presented an increase in Qs/Qt values, in the immediate postbypass period (T1), and P(A-a)O2 values significantly increase comparing basal versus T1 and T2 values. In all the three groups the respiratory system resistance and AUTO-PEEP values were unchanged after the end of CPB. The comparison between the groups showed a significant minor impairment of gas exchange (PaO2 and P(A-a)O2), Qs/Qt and Cstat in the third group of patients. These results show that lungs inflation with air during CPB, effectively preserve respiratory system mechanics: this might be due to a preservation of bronchial perfusion simply due to the mechanic expansion of the lung otherwise compromized when the lungs are completely collapsed. However it is necessary to emphasize that CPB has negative effects on gas-exchange whatever technique of lung management is used.