Purpose: Rapid activation of the cardiac catheterization laboratory (CCL) is fundamental in the treatment of ST-segment elevation myocardial infarction (STEMI), and it is recommended that emergency department physicians activate CCL as soon as possible, however false positive activation is a major concern. The aim of this study is to assess the relationship between false positive activation and clinical factors available at the time of diagnosis. Methods: All subjects with CCL activation by an emergency physician between August 2009 and May 2012 were included in this study. False-positive CCL activation was defined as absence of a clear culprit lesion on coronary angiography or by assessment of electrocardiographic and biomarker data in the absence of angiography. Results: Of 222 STEMI activations by emergency physicians, 55 (25%) were false-positive STEMI. Coronary spasm, cardiomyopathy, known CAD, and heart failure were the most common diagnoses among false-positive STEMI. A history of cardiomyopathy (adjusted odds ratio, 13.393; 95% CI, 2.550-70.334; p=0.002), systolic blood pressure<100 mmHg at presentation (adjusted odds ratio, 2.817; 95% CI, 1.129-7.026; p=0.026), no chest pain on admission (adjusted odds ratio, 2.460; 95% CI, 1.162- 5.209; p=0.019), and prior coronary disease (adjusted odds ratio, 3.966; 95% CI, 1.828-8.606; p<0.001) independently increased the odds of false-positive STEMI activations. Conclusion: False-positive CCL activations were relatively common according to the definition in this study. Various patient-level characteristics were significantly associated with false-positive CCL activation.