Background: Although elevated serum fibrinogen and Lp(a) are known to be associated with coronary atherosclerosis and AMI with thrombus formation, the association between the elevated level of fibrinogen or Lp(a) and coronary spasm remains to be elucidated. The purpose of this study is to determine whether the elevation of serum fibrinogen and Lp(a) is a risk factor for coronary spasm and also for the development of AMI in patients with coronary spasm. Methods: Consecutive 231 patients documented coronary vasospasm but without a significant stenosis (>50%) by ergonovine provocation test were divided two groups, angina pectoris (group I; n=202, 49.5짹11.1 years) and acute myocardial infarction (group II; n=29, 47.4짹11.2 years). Results: Baseline clinical characteristics were not different between the two groups. The serum Lp(a), fibrinogen, hsCRP, apolipoprotein A1/B ratio were measured in all patients. The levels of Lp(a), hsCRP, fibrinogen were higher (respectively, p<0.029, p<0.002, p<0.000) in group II (29.6짹24.8 mg/dl, 1.88짹2.9 mg/dl, 317.5짹51.2 mg/dl) than in group I (21.2짹17.8 mg/dl, 0.68짹1.5 mg/dl, 263.2짹70.3mg/dl), but Apo(A1/B) level was lower (p<0.03) in group II (0.66짹0.21) than in group I (0.87짹0.37). Multivariate analysis demonstrated that higher fibrinogen level is an independent determinant for AMI in these patients (odds ratio=8.35; 95% CI=1.94 to 30.0). Conclusions: Elevated level of fibrinogen is associated with MI in patients with coronary spasm, suggesting that fibrinogen may play an important role in the genesis of thrombotic coronary occlusion subsequent to coronary spasm.