An electrophysiology study is performed to evaluate the electrical activity of the heart. The purpose of the electrical system of the heart is to coordinate the pumping of the four chambers of the heart and to control the heart rate so that the heart speeds up and slows down as the demands of the body change. The SA node starts the electrical signal. The electrical signal then travels through the atria causing them to contract. Then it passes through the AV node, the bundle of His, and bundle branches and then out to the muscle fibers of the ventricles. As the impulse spreads, the muscles contract and the ventricles pump. To perform an electrophysiology study, three to five electrically sensitive catheters are placed inside the heart to record electrical activity. These recordings locate abnormal tissue that causes irregularities in the heartbeat (arrhythmias).