Background: Tissue factor (TF) is a low molecular weight glycoprotein that serves as primary initiator of extrinsic coagulation cascade and major regulator of coagulation, hemostasis and thrombosis, therefore TF is the major source of thrombin production in vivo and may play an important role in the pathogenesis of ischemic coronary syndromes by mediating intravascular thrombosis. Methods and results: TF levels were measured in 15 patients with acute myocardial infarction (AMI) (within 6 hours after the onset of symptoms), 10 patients with unstable angina, 10 patients with stable exertional angina and 10 healthy controls. Five patients with AMI had a history of unstable angina before infarction and 10 had a sudden onset of infarction. The plasma TF level was higher in the AMI group than in the unstable angina, stable exertional angina and control groups (298.3 + 30.63 vs 285 + 11.32 pg/ml [P <0.001] vs 190 + 17.6 pg/ml [p < 0.001] vs 179 + 17.8 pg/ml [p < 0.001] respectively). TF levels were decrease in chronic phase (2 weeks after admission) compared with acute phase of infarction (from 298.3 + 30.63 pg/ml to 275 + 31.28 pg/ml, P <0.001). in addition, plasma TF levels were higher in patients wither AMI with prodromal unstable angina than in patients with sudden onset of infarction (328 + 12 pg/ml vs 283.5 + 25.7 pg/ml, p < 0.001). TF levels were similar in the acute and chronic phases in the patients with AMI with prodromal unstable angina (328.2 + 12 pg/ml vs 303 + 14.8 pg/ml, p = 0.3) and were similar in the acute and chronic phases in the patients with AMI with sudden onset of infarction (283.5 + 25.7 pg/ml vs 261 + 27.7 pg/ml p = 0.1). TF levels had no significant correlation with the peak levels of cretin kinase (CK) (IU/L) and creatine kinase-MB (CK. MB) (IU/L) (298.3 + 30.63 pg/ml vs 1929.6 + 898.61 IU/L p = 0.2 vs 103.6 + 74.27 IU/L p=0.3 respectively). TF levels had no significant correlation with all motion score index either on admission or after 2 weeks (298.3 + 30.63 pg/ml vs 1.4 + 0.16 p = 0.1 vs 1.4 + 0.16 p = 0.09 p = 0.8 vs 0.3 + 0.05 p = 0.7 respectively). TF levels were higher in AMI patients complicated by postinfarction angina than in non complicated patients (303 + 13.2 pg/ml vs 290.4 + 28.64 pg/ml p <0.008). TF levels in AMI patients had significant correlation with the number of coronary arteries occluded by more than 70% (298.3 + 30.63 pg/ml vs 2.47 + 1.35 p <0.001). Conclusion: Significant elevation of plasma TF level is a constant finding in our patients with ACS and plaque disruption appears to be a potent stimulus for its production and release. The magnitude of myocardial damage is not determined by plasma TF levels. Plasma TF levels are related to the number of coronary vessels occluded by more than 70%. However, elevated level in the early post-infarction period adversly affect the clinical outcome and may be predictors of a subset group of patients with subsequent worse outcome.