An electrophysiology study (EPS or EP study) is a test used to better understand the electrical system of the heart. Patients undergo an EPS for many reasons; they can have either fast or slow heart rhythm abnormalities (arrhythmias), have extra beats from either the upper chambers (atria) or lower chambers (ventricles) of the heart, have passing out episodes (syncope), or have episodes when they almost pass out (near-syncope). The EP study is performed by a board certified physician trained in all aspects of arrhythmia recognition and management (electrophysiologist). Small thin wires coated with plastic (catheters) that contain metal rings (electrodes) on them are placed through veins (typically in the groin). The physician moves these catheters into the heart using x-ray guidance. These catheters allow electrical measurements to be made from inside the heart and allow the heart muscle to be stimulated. This helps the electrophysiologist determine the state of the electrical system of the heart as well as the presence of any arrhythmias.