Potential etiologic factors of postcardiopulmonary bypass (post-CPB) lung edema (LE) were investigated (phase 1 study). Further patient treatment was modified according to the results of phase 1 study and the influence that these changes had on the incidence of the complication was assessed (phase 2 study). In phase 1 study, among 100 patients who underwent coronary bypass graft surgery, prolonged assisted ventilation was required for severe LE in 7 cases, and 6 patients had a moderate form of LE. Patients who suffered from severe LE had left and right ventricular dysfunction and normal pulmonary vascular resistance. Three predictors of LE were evidenced by logistic regression analysis: number of bypass grafts completed with internal mammary arteries (p = 0.013), transfusions of blood collected in mobile units (p = 0.014), and the combination of a significant lesion of the left main stem and the right coronary artery at preoperative angiography (p = 0.040). In phase 2 study, a further group of 100 patients was treated differently by improving myocardial protection during surgery, achieving a higher rectal temperature at the end of CPB, and reducing the amount of transfusions. This resulted in only one case of LE (p < 0.001). In conclusion, the cases of post-CPB LE evidenced in our study were related to postoperative ventricular dysfunction and blood transfusions. Any means of improving postoperative hemodynamic stability and reducing the need for transfusions could thus prevent the latter complication.