Cardiac catheterization is the method doctors use to perform many tests available for diagnosing and for treating coronary artery disease. Cardiac catheterization is used with other tests such as angiography and electrophysiology studies (EPS). The method involves threading a long, thin tube (called a catheter) through an artery or vein in the leg or arm and into the heart. Depending on the type of test your doctor has ordered, different things may happen during cardiac catheterization. For example, a dye may be injected through the catheter to see the heart and its arteries (a test called angiography), or electrical impulses may be sent through the catheter to study irregular heartbeats (tests called electrophysiology studies).