**1. Introduction**

Cardiac electrophysiology study (EPS) is helpful to assess the heart's electrical system. This is an invasive percutaneous cardiac procedure used for the investigation and treatment of certain arrhythmias. During the examination, catheters are inserted to the appropriate position within the heart mainly via large veins to record the electrical signals of the heart and to pace from different localized areas. In this way, EPS can help evaluating the function of the conduction system, determining the mechanisms of brady- and tachyarrhythmias, and identifying areas which may be the targets of often curative catheter ablation. Many cardiac arrhythmias that previously required the use of potentially harmful antiarrhythmic drugs can now be routinely cured in the electrophysiology laboratory by means of transcatheter ablation techniques.

In this chapter, the basics of cardiac electrophysiological studies are presented.
