Introduction Acute myocardial infarction is the most dangerous manifestation of ischemic heart disease and is usually caused by atherosclerotic plaque disruption in the coronary artery wall. Copeptin has been proposed as a prognostic marker in different illnesses and disorders where it may help in early detection and diagnostic accuracy. Objective The aim of this study is to examine the diagnostic efficacy of identifying copeptin in acute myocardial infarction (AMI). Study outline The study is organized as a cross-sectional research (prospective pairedresearch). Participants and Methods Participants (N=73) were divided into two groups: patients with NSTEMI AMI (N=37) and controls (N=36). Medical history and ECG were taken for all participants. TroponinI (TnI) concentrations were measured by chemiluminescence immunoassay based on LOCI technology on Dimension ExL with LM analyzer (Siemens Healthcare Diagnostics Inc., Newark, USA). CK and CKMB concentration were measured on the Beckman Coulter AU 680 analyzer (Beckman Coulter Inc., Brea, USA). CK was measured by enzymatic assay (Beckman Coulter) and CKMB by enzymatic immunoinhibitoryassay (Beckman Coulter). Copeptin concentrations were measured by enzyme-linked immunosorbentassay(ELISA) on the Labsystems IEMS Reader MF (LabsystemsOy, Helsinki, Finland) analyzer. The results were processed by a statistical program (MedCalc Software, Mariakerke, Belgium). Results The median values for the copeptin and CK did not differ between the groups. The median values of CKMB and troponin I were higher in patients with NSTEMI AMI than in control subjects; CK MB: 17 ng/L vs. 14 ng/L (P=0.025); TnI: 0.037 ng/L vs. 0.009 ng/L (P=0.001). CKMB showed a higher specificity compared to copeptin(88.9% versus 25.0%), while copeptinshowedhigher sensitivity compared to CK MB (96.6% versus 37.9%) in NSTEMI AMI diagnosis. Conclusion Copeptinconcentrations did not differ between the two observed groups. Thus, it can be concluded that copeptin did not show satisfactory score for NSTEMI AMI exclusionin early onset of the symptoms.