Cardiopulmonary bypass (CPB) induces hemolysis, which manifests as plasma free hemoglobin. We investigated in a post hoc analysis of a single-center, blinded, controlled study whether the use of a novel hemoadsorption device (CytoSorb, CytoSorbents Europe GmbH, Berlin, Germany) affects hemolysis during CPB. A total of 35 patients undergoing elective CPB surgery with an expected CPB duration of more than 120 min were included in the analysis. The hemoadsorption device was used in 17 patients (intervention group) and not used in 18 patients (control group). The primary outcome was differences of postoperative free hemoglobin and haptoglobin levels. As secondary outcomes, we investigated differences in postoperative lactate dehydrogenase and bilirubin levels. Postoperative free hemoglobin levels were not significantly different between the groups. However, there were statistically significant differences between the treatment and control groups in the median levels of haptoglobin (58.4 vs. 17.9 mg/dL, respectively; P < 0.01) and lactate dehydrogenase (353.0 vs. 432.0 U/L, respectively; P < 0.05) on postoperative day 1. Thus, in this study, we did not find an effect on hemolysis in patients treated with hemoadsorption, though lower haptoglobin level and higher secondary hemolysis markers on postoperative day 1 in patients not treated with the hemoadsorber may be an indication of some moderate effect of the device. Studies with larger samples are needed to clarify the significance of the small differences detected in this study.