Backgrounds Periprocedural myonecrosis is a frequent occurrence in percutaneous coronary intervention(PCI). Several studies have corroborated the relationship between periprocedural MI and clinical outcomes. Clopidogrel pre-treatment was understood to decrease periprocedural ischemic events. We evaluated method of clopidogrel pre-treatment undergoing conventional coronary angiogram to reduce periprocedural myonecrosis in angina patients. Methods Between October 2010 and July 2011, 386 PCI patients who were admitted with angina pectoris to Korea University Anam hospital, Eulji hospital, and Hanil hospital were included. 241 clopidogrel naïve patients with scheduled PCI were enrolled loading group (clopidogrel 600mg loading before at least 2hrs to 24hrs). 145 patients on chronic therapy with clopidogrel 75mg/day were randomized to additional 300mg reloading (reload group, N=72)) or no additional loading (chronic use group, N=73). CK-MB levels were measured at baseline, 8hrs, and 24hrs after PCI. Troponin I was measured at 8hrs. hs-CRP and VerifyNow (P2Y12) were measured before PCI. The definition of periprocedural myonecrosis is a CK-MB elevation > 3 times the upper limit of normal (ULN). Results After exclusions due to baseline CK-MB elevation, total 192 patients (Loading N=96, Reload N=48, Chronic use N=48) were analyzed. Periprocedural myonecrosis were occurred only 4 cases (Loading 3, Reload 1, Chronic use 0) (P=0.646). There is no significant difference of mean CK-MB at baseline, 8hrs and 24 hrs after PCI among 3 groups (P=0.555, 0.221, 0.108, respectively) (figure). There is no significant difference of 8hrs Troponin I and PRU (p2y12 reaction units) values among 3 groups (P=0.350, 0.226, respectively). Conclusions Pre-treatment with 600mg loading dose of clopidogrel before conventional PCI showed similar occurrence of periprocedural myonecrosis, as compared with chronic clopidogrel use or 300mg dose reloading treatment. There is no significant difference of PRU value according to pre-treatment methods.