Background. Copeptin is a new prognostic marker of future cardiovascular death or heart failure in patients with acute coronary syndrome. Methods. We collected 57 arterial blood samples at the ascending aorta during primary percutaneous coronary intervention (PCI) in acute ST elevation myocardial infarction (STEMI). We assessed commonly used cardiac biomarkers[CK, CK-MB, troponin-I, CRP] and additionally measured the recently introduced biomarkers [Copeptin(C-terminal Provasopressin), NT-proBNP]. Intravascular ultrasound (IVUS) imaging was performed before and after stent implantation during primary PCI. Results. Pt age was 59짹12 yrs and 94% were males. IVUS imaging of the culprit lesion was amenable in 55 pts who were divided into 2 groups depending on the presence of ruptured plaque: ruptured plaque (22 pts) and non-ruptured plaque (33 pts). Greyscale IVUS showed vessel size, minimal lumen area(MLA) and plaque area were larger in ruptured plaque, however the lesion length was similar(p=0.178)(Table). Overall all of cardiac biomarkers were increased, especially Copeptin was higher in ruptured plaque than non-ruptured plaque (p=0.045). While troponin I, CK-MB, CRP was not correlated with Copeptin, NT-proBNP was correlated with Copeptin (r=0.579, p=0.0003). Vessel size and MLA were not correlated with Copeptin(r=0.05, p=0.743 and r=0.130, p=0.388, respectively). Conclusions. Stress stimulated Copeptin might be one of the prognostic factor to plaque rupture. The potential role of Copeptin deserve further study in acute myocardial infarction.