This is an open-label phase 2 study recruiting low, moderate, and high likelihood ACS patients from approximately 60 centers. Patients will be imaged with iodofiltic acid I 123 for the detection of myocardial ischemia. Readers independent of the clinical study centers will review results of imaging studies in a blinded fashion at an imaging core lab. The resulting independent reading of the images will be compared against the truth standard for ACS.