EP testing is a highly accurate and safe means of mapping the heart's electrical system and identifying the exact pathways that are functioning incorrectly in your heart to cause an arrhythmia. The study will also help to determine how the arrhythmia responds to treatment. Unlike the tests listed above, this test is invasive and involves the insertion of thin, flexible tubes called electrode catheters into your heart. The catheters are placed in a vein in your groin and advanced to the right atrium and ventricle of the heart, using an x-ray imaging technique called fluoroscopy to guide them. Your doctor then tries to stimulate the part of your heart that is causing the arrhythmia. After the diagnostic portion of the EP test, your doctor may decide to perform a therapeutic procedure such as ablation or implantation of a pacing device.