Fibrinopeptides A and B (FPA and FPB) are short amino acid sequences situated at the amino termini of the alpha and beta chains (respectively) of soluble fibrinogen. Fibrinopeptide A is a 16-amino acid cleavage product of thrombin-induced proteolytic cleavge of fibrinogen. Liberation of FPA and another 14-amino acid peptide, fibrinopeptide B, uncovers the E domain of fibrinogen. The residual protein, fibrin monomer, polymerizes to form fibrin clot. Thus, liberation of approximately 4 ng/ml of FPA per milligram of fibrinogen is closely linked to clot formation. Because proteolysis of fibrinogen accelerates early after the onset of thrombosis, marked elevations in FPA levels are expected early after the onset of clotting. Elevation of Fibrinopeptide A levels in plasma is seen in association with disorders such as disseminated intravascular coagulation, deep venous thrombosis, arterial thrombosis, and malignancy. Given the short half-life of FPA in plasma (3-5 min) and the conversion of fibrinogen to fibrin is particularly rapid and early during the course of thrombosis, measuring for elevated FPA levels in samples obtained very early after the onset of symptoms of transmural infarction would be beneficial to assess association with acute coronary thrombosis. Elevated FPA levels appear to be a marker during the course of coronary thrombosis.