Interleukin (IL)-6 is a pleiotropic inflammatory cytokine with both pro- and anti-inflammatory capacities, produced by different cells and tissues, such as leukocytes, adipocytes, and endothelium. From the viewpoint of cardiologists, this cytokine is a reliable biomarker of cardiac dysfunction, occurrence of atrial fibrillation, cardiac myxoma with recurrence, remote metastasis or embolization, and atherosclerotic processes. Although IL-6 levels were detected in patients undergoing cardiac operations and reported sporadically, the perioperative kinetics of IL-6 in cardiac surgical patients was insufficiently elaborated. The influencing factors, clinical implications, and causative effects of IL-6 on clinical outcomes and potential treatment choices among cardiac surgical patients remained to be clarified as well. The purpose of this article is to discuss these aspects of IL-6 in patients undergoing a cardiac operation.