Electrophysiology study (EPS)–A procedure performed in a special lab in the hospital; the study attempts to reproduce an abnormal heart rhythm. Electrophysiology testing provides the most accurate diagnosis of arrhythmias. EPS is a safe, fast (usually one to two hours), and relatively comfortable procedure. A patient undergoing an electrophysiology test is sedated and catheters are placed through small intravenous tubes into a vein or artery and fed to the heart. Electrophysiologists use the catheters to monitor the heart’s response to electrical stimuli. By stimulating different parts of the heart’s conduction system, an electrophysiologist can determine the source and type of an arrhythmia. X-ray cameras allow the electrophysiologist to view and properly guide the insertion of the catheters. The catheters allow the electrophysiologist to measure and record electrical activity from an internal source and compare it against external recordings from electrodes placed on the patient’s chest and back.