Soluble fibrin monomer appears in the bloodstream during the extremely early stage of blood coagulation and generally forms a complex with fibrinogen, termed soluble fibrin monomer complex (FMC). Determination of FMC can provide information regarding the state of thrombotic diseases; thus it is important to investigate whether FMC serves as an early indicator of myocardial infarction (MI). We investigated hemostatic and fibrinolytic parameters including FMC to determine their capabilities for indicating thrombotic conditions in the coronary artery. Blood samples from 47 patients with acute MI were obtained within 48 hours (acute phase) and during 120 - 600 hours (recovery phase), respectively, after MI onset. Plasma FMC was significantly elevated in the acute phase, compared with that during the recovery phase and in healthy controls (p = 0.001), suggesting that its elevation indicates thrombotic events in the coronary artery of MI patients. D-dimer, a marker of thrombus formation accompanied with fibrinolysis, was increased in both phases in the patients. In addition, FMC and D-dimer were significantly increased within 24 hours after onset as compared to 24 - 48 hours (p = 0.003 and p = 0.011). Furthermore, cardiac troponin T, a marker of myocardial damage, was significantly higher after 24 hours than within the first 24 hours (p = 0.001). Receiver operating characteristic (ROC) analysis of FMC for early MI diagnosis indicates that FMC, rather than D-dimer, is a better marker within 24 hours of onset. Measuring plasma FMC may be useful for early diagnosis of MI recurrence and deciding primary treatment.