Graphical AbstractPatients presenting with an acute coronary syndrome were randomized 1:1 to placebo or to 420 mg of evolocumab within 24 h of hospital admission. Biomarkers of platelet activation and endothelial dysfunction were measured at baseline (before randomization) and 30 days. Administration of evolocumab was associated with decreased levels of platelet factor 4 (PF4) and von Willebrand factor (vWF). In arterial specimens of participants undergoing coronary artery bypass surgery, there was a decreased interaction among PCSK9, platelets, and endothelial cells in the evolocumab group.