Objective: The damage occurred during cardiopulmonary bypass (CPB) by activated leukocytes is a common problem in open-heart surgery and may cause postoperative morbidity. Several techniques have been investigated to limit these damaging effects of leukocytes. One of these is leukocyte filtration during CPB either systemically through the arterial or venous line of the bypass circuit or through the cardioplegic solution. We studied the effects of systemic arterial line filtration during reperfusion period, on early postoperative heart functions. Material and Methods: Thirty patients scheduled for an elective coronary artery bypass grafting were registered for the study and they were divided equally into 2 groups as control and systemic leukocyte filtration through the arterial line of the CPB circuit. Conventional arterial line filter was used in the control group while in the leukocyte filtration group, a commercially available leukocyte filter and a conventional arterial line filter were parallely incorporated into the CPB circuit. Blood passed through the arterial line was filtered during the reperfusion phase and the rest of the CPB duration. Results: Preoperative and intraoperative data obtained from the participants did not reveal any differences between groups. Similarly no statistically significant difference was present in terms of complete blood count, duration of mechanic ventilation, and length of intensive care unit and hospital stay. Intrapulmonary shunt calculations at postoperative hour 1 (11.64 ± 2.80% vs. 9.17 ± 1.82%, p= 0,02), and arterial oxygen pressure (74.20 ± 8.24 mmHg vs. 81.80 ± 10.04 mmHg, p= 0.04), respiratory rate (24.27 ± 2.05 breath/min vs 22.20 ± 3.14 breath/min, p= 0.02), alveolar-arterial oxygen differences (138.73 ± 44.87 mmHg vs 131.37 ± 28.70 mmHg, p= 0.04) and oxygenization index (353.33 ± 39.23 vs 389.52 ± 47.83, p= 0.05) measurements at postoperative hour 24 were significantly better in the leukocyte filtration group. Conclusion: We concluded that, in the elective coronary artery bypass grafting patients, leukocyte filtration through the arterial line during the reperfusion period did not reduce the white blood cell count in the peripheral blood adequately. Moreover, although filtration performed in this fashion may reduce lung damage, this effect is temporary in nature and does not extend beyond 24 hours of operation, and does not provide an evident clinical benefit. Copyright © 2006 by Türkiye Klinikleri.