Troponin I is a sensitive marker of myocardial necrosis, which will be elevated due to an intraluminal coronary thrombus related to atherosclerotic plaque rupture or other spontaneous coronary artery disease (CAD) event (MI Type I). STEMI patients will be excluded from this study. The scope of this study will be limited to the rule-in and rule-out of NSTEMI in ER patients with suspected ACS and no other known causes for elevated troponin.