To determine if the American College of Cardiology (ACC) cardiac monitoring guidelines accurately stratify patients according to their risks for developing clinically significant arrhythmias in non-intensive-care settings, we conducted a prospective cohort study of 2,240 consecutive patients admitted to a non-intensive-care telemetry unit over 7 months. Sixty-one percent of patients were assigned to ACC class I (telemetry indicated in most patients), 38% to class II (telemetry indicated in some), and 1% to class III (telemetry not indicated). Arrhythmias were detected in 13.5% of the class I patients, 40.7% of the class II patients, and 12% of the class III patients (p < .001). Telemetry detected an arrhythmia resulting in transfer to an intensive care unit in 0.4% of the class I patients, 1.6% of the class II patients, and none of the class III patients (p = .006). Telemetry led to a change in management for 3.4% of the class I patients, 12.7% of the class II patients, and 4% of the class III patients (p < .001). When patients with chest pain as the reason for admission were moved from class I to class II and patients with arrhythmias as the reason for admission were moved from class II to class I, more arrhythmias and more clinically significant arrhythmias occurred in class I patients and the trends from class I to class III were more consistent with the purpose of the guidelines. These findings indicate that when the ACC guidelines are reexamined, consideration should be given to changing them so they are more useful in non-intensive-care settings.