Acute coronary syndromes are characterized by increased endothelial activation. The aim of this study was to investigate the behavior of coagulation factors V, VII, VIII and normal inhibitors antithrombin III and protein C during the acute phase of myocardial infarction. Thirty-six patients (27 men, nine women) and 35 normal individuals were studied during the acute phase of myocardial infarction, in the first 24 h. A group of 35 normal individuals was used as a control group. Blood samples were taken within the first 24 h of the hospital admission. The plasma levels of the coagulation factors were measured by the clot formation method, whereas the normal inhibitors were measured by ELISA. In the acute phase of myocardial infarction significant changes occur in coagulant and fibrinolytic factors. A decrease in plasma levels of factor V, antithrombin III and protein C was found in patients with acute myocardial infarction, compared to control group, whereas an increase in plasma levels of factor VII were observed. This study concludes that acute myocardial infarction causes consumption of fibrinolytic factors, whereas the coagulant factors seem to increase when being activated.