Sometimes your heart's electrical system must be studied with an intracardiac (within the heart) electrophysiologic procedure (EP). This test is similar to a cardiac catheterization. One or more catheters are moved through the blood vessels into the heart. There they record electrical signals from inside the heart. This gives much more precise information than an ordinary ECG. During this study, the heart can be stimulated to beat rapidly or irregularly. The heart's response and the way the electricity moves around the heart during an arrhythmia help the cardiologist diagnose the cause and nature of an arrhythmia.