The results for platelet count (PC), activated clotting time (ACT), postoperative bleeding, and hemoderivatives usage in cardiac surgeries were crossed against the type of oxygenator used. These were two bubble and one membrane type. A sample of the surgery population for each type was selected at random. Thus, the patients in this study were divided into 3 groups: BA: 87 patients, bubble oxygenator; BB: 87 patients, bubble oxygenator; M: 73 patients, membrane oxygenator. The groups were statistically similar (p > 0.05) for age, body surface area, cardiopulmonary bypass (CPB) time, and prevalence of cardiac disease. The rate of PC 15 min after CPB end and before its beginning was BA, 0.48 +/- 0.02; BB, 0.49 +/- 0.02; M, 0.55 +/- 0.03. The rate of ACT after protamine administration and before CPB was BA, 1.22 +/- 0.03; BB, 1.16 +/- 0.03; M, 1.16 +/- 0.03. Volume (ml) of total postoperative bleeding (POB) was BA, 904 +/- 72; BB, 963 +/- 73; M, 867 +/- 83. Patient percentage that used hemoderivatives (HD) was BA, 86.3%; BB, 88.5%; M, 90.0%. No statistical difference was found between groups (p > 0.05). This study indicates that although membrane oxygenators have better theoretic and experimental biocompatibility, no significant difference in PC, ACT, POB, and HD usage was observed in the clinical setting. All values are expressed as the mean +/- standard error of the mean.