Most patients and their families, and even most doctors, are confused about what cardiac electrophysiology is all about. Electrophysiology is the process of identifying the type of arrhythmia, the point of origin of the arrhythmia, and the specific pathogenesis of the arrhythmia through the use of certain tests. Once these issues have been determined, more targeted and effective treatment can be provided. Common electrophysiologic tests can be performed by pacing with electrodes delivered into the esophagus or by inserting a catheter into the cardiac chambers. Esophageal pacing is performed by inserting a thin catheter with electrodes into the esophagus (the front of the esophagus next to the back of the heart) through the nasal cavity, which can be used to detect abnormalities of the heart’s pacing and conduction in the same way that scouts enter the entrance of an enemy stronghold. This method is generally used to diagnose patients with preexcitation syndrome, paroxysmal supraventricular tachycardia, and sick sinus node syndrome. Intracardiac electrophysiology is often used for some complex arrhythmias, or for some patients with arrhythmias that require radiofrequency ablation, or pacing therapy. At that time, special catheter electrodes are inserted into the blood vessels up to the heart chambers, and after the examination determines its source, the interventional procedure can be performed immediately. Examples include paroxysmal tachycardia, atrial fibrillation, and atrioventricular block.