Current literature suggests that a large proportion of chest X-rays (CXRs) performed in emergency department (ED) patients with chest pain and suspected acute coronary syndrome (ACS) are unnecessary. The Canadian ACS Guidelines aim to guide clinicians in the appropriate use of CXR within this patient population. This study determined the prevalence of clinically significant CXR abnormalities and assessed the utility of the guidelines in a population of ED patients with chest pain and suspected ACS. Included in the study were participants over the age of 18 who presented to an Australian metropolitan ED, over a 1-year period, with a primary complaint of chest pain and who had a CXR and troponin level ordered in the ED (N=760). We retrospectively compared their radiographic findings with their recommendations for CXR according to the ACS Guidelines. We found that 12 of the participants had a clinically significant chest X-ray. The guidelines had a sensitivity of 80 (95 CI 0.70-0.87) and specificity of 50 (95 CI 0.47-0.54). The positive predictive value was 18 (95 CI 0.15-0.22) with a 95 negative predictive value (95 CI 0.92-0.97). Had the ACS guidelines been applied to our patient population, the number of CXR performed would have been reduced by 47 . This study suggests that the ACS Guidelines has the potential to reduce the numbers of unnecessary CXR performed in ED patients. However, this would come at the expense of missing a minority of significant CXR abnormalities.