Objective: In accordance with the AHA/ACC clinical practice guideline, the likelihood of acute ischemia caused by coronary artery disease (CAD) is to be determined as high, intermediate, or low for all patients presenting with chest discomfort. This study was conducted to estimate extent of significant CAD in patients with high and intermediate likelihood of unstable angina (UA) according to “AHA likelihood classification” Materials and Methods: Overall, 133 consecutive patients presented with symptoms or signs suggestive of UA, which was classified as of high or intermediate likelihood in Emergency Department (ED), and undergoing coronary angiography (CAG) within one week were enrolled into the study. The characteristics of the patients in either subgroup were compared in terms of the findings of the CAG. Results: In patients with high likelihood of UA (n=89), CAG revealed that 62 had significant CAD, 7 - moderate CAD, 20 - mild CAD or normal coronary angiogram. In patients with intermediate likelihood of UA (n=19), CAG revealed that 2 patients had significant CAD, and 17 - mild CAD or normal coronary angiogram. The rate of significant CAD was significantly higher in patients with high likelihood (p<0.001, LR 23.97, 95% CI 4.21-90.43). The sensitivity and specificity of having at least one of high likelihood features for detecting significant CAD were found to be 96.8% and 38.6% respectively. Conclusion: We suggest that the likelihood classification is useful for the triage of the UA patients in the ED. When supported with further studies, utilization of this classification will yield a high diagnostic accuracy in predicting or ruling out severe CAD in patients presenting with chest pain.