Background: Coronary artery spasm (CAS) at the myocardial bridge (MB) segment has been proposed as a possible factor resulting in adverse clinical events. There is limited data whether the longer MB length can be associated with more significant CAS or not. We evaluated the angiographic and clinical parameters according to MB length during acetylcholine (Ach) provocation test. Methods: A total 247 consecutive patients (pts, 141 men; mean age 57.01짹11.87 years) with MB underwent the Ach provocation test by incremental doses of 20, 50, 100 ug into the left coronary artery were enrolled from March 2004 to April 2009. The MB pts were divided in to two groups according to MB length. The Ach provocation test results and its associated parameters were compared between the short MB length group (���20mm, n=110) and long MB length group (>20mm, n=137). Results The baseline clinical characteristics were balanced except more male gender (45.5% vs 66.4%, p=0.001) and hyperlipidemia (22.7% vs 38.7%, p=0.009) in the long MB length group. The incidence of ischemic chest pain and ST-T change were not different between the two groups. There was a trend toward higher incidence of diffuse CAS in the long MB length group but the the incidence of MB narrowing, baseline spasm (Table). Conclusion: In our study, there was a trend toward higher association of diffuse CAS with longer length of MB, suggesting the longer the MB length, the higher likelihood of diffuse severe CAS in clinical presentation.