SIGNIFICANT POSTOPERATIVE BLEEDING is a common risk of cardiac surgery, with approximately 3.5% of patients requiring surgical re-exploration.1 Re-exploration is associated with adverse outcomes, including infections, ischemia, and increased 30-day mortality.2 Similar adverse outcomes are related to erythrocyte transfusions associated with cardiac surgery,3 in addition to the immunologic and administrative hazards of transfusion.4 These risks are important because the majority of patients undergoing cardiac surgery receive a blood transfusion despite the lack of evidence to support liberal transfusion strategies.5 The frequency and significance of bleeding after cardiac surgery warrant investigation of the hematologic changes throughout the procedure. This review focuses on the (patho)physiology of platelet-derived microvesicles in the setting of cardiovascular surgery, a developing area in the understanding of the control of coagulation.