Thrombotic occlusion of an epicardial coronary artery on the grounds of atherosclerotic plaque is considered the ultimate step in AMI (acute myocardial infarction). However, the precise pathophysiological mechanisms underlying acute coronary occlusion are not fully understood. We have analysed proteomic profiles of systemic plasma and plasma derived from the site of coronary plaque rupture of non-diabetic patients with STEMI (ST-segment elevation myocardial infarction). Label-free quantification of MS/MS (tandem MS) data revealed differential regulation of complement cascade components and a decrease in anti-thrombotic PEDF (pigment epithelium-derived factor) between CS (culprit site)-derived plasma and systemic plasma. PEDF, which is known to have a protective role in atherothrombosis, was relatively decreased at the CS, with a level of expression inverse to local MMP-9 (matrix metalloproteinase-9) activity. CS plasma displayed enhanced proteolytic activity towards PEDF. Proteomics of coronary thrombus aspirates indicate that PEDF processing is associated with coronary plaque rupture.