As cardiac arrhythmia services and the ability to perform electrophysiologic testing become more prevalent in the hospital setting, advanced practice nurses (APNs) are continually challenged to keep their skills in evaluating patients with dysrhythmias sharp and current. The experienced APN evaluates the patient's history, recognizes physical findings, and uses noninvasive data to help diagnose, anticipate, and even prevent dysrhythmias. This article reviews the essential components of a systematic evaluation of patients with a known or potential rhythm disturbance.