Background: Vasospastic angina is suspected when coronary angiography fail to show a culprit lesion in a patient with typical chest pain. Intracoronary (IC) nitroglycerine (NTG) infusion often induces modest vasodilation in coronary arteries at provocation test but its clinical significances are not elucidated yet. Methods: A total of 1764 consecutive patients (pts) who underwent coronary angiography with Ach provocation test were enrolled from January 2004 to august 2010. Ach provocation test was performed by IC infusion with incremental dosage (20, 50, 100µg). Vasoconstriction more than 70% by visual assessment was considered as positive. Baseline spasm was defined as diffuse coronary vasodilation more than 30% after IC NTG infusion as compared to initial angiogram. We investigated its impact on acetylcholine (Ach) provocation test results. Results: There were no significant differences in baseline characteristics between 2 groups except alcohol consumption history was higher in the basal spasm group (31.5% vs. 36.5%, p=0.030). One third (34.9%, 456/1308) of the study population showed baseline spasm. Baseline spasm group showed higher incidence of chest pain during the test, positive provocation test result, response to lower Ach dose, multi-vessel involvement, and more severe vasoconstriction (> 70%) by QCA analysis (Table). Conclusions: According to our study, presence of baseline spasm was considered as an important prognostic factor of positive Ach provocation test and may be an indicator of hyperreactivity of coronary artery to Ach provocation, which represents severe endothelial dysfunction.