The most accurate method (the "gold standard") for evaluating and defining coronary artery disease (CAD). Coronary angiography is used to identify the exact location and severity of CAD. During coronary angiography, a small catheter (a thin hollow tube with a diameter of 2-3 mm) is inserted through the skin into an artery in the groin or the arm. Guided with the assistance of a fluoroscope (a special x-ray viewing instrument), the catheter is then advanced to the opening of the coronary arteries, the blood vessels supplying blood to the heart. Next, a small amount of radiographic contrast (a solution containing iodine, which is easily visualized with x-ray images) is injected into each coronary artery. The images that are produced are called the angiogram. Angiographic images accurately reveal the extent and severity of all coronary arterial blockages. Coronary angiography is performed with the use of local anesthesia and intravenous sedation, and is generally not terribly uncomfortable. The procedure takes approximately 20-30 minutes. After the procedure, the catheter is removed and the artery in the leg or arm is sutured, "sealed," or treated with manual compression to prevent bleeding. There is a small risk of serious complications from coronary angiography, as it is an "invasive" test, but in the hands of an experienced physician, this risk is quite small (well below one per cent). In patients for whom the test is appropriate, the therapeutic information learned from the coronary angiogram is far more valuable than the relatively small risk of the procedure. For patients with severe angina or myocardial infarction, or those who have markedly abnormal noninvasive tests for CAD, the angiogram also helps the doctor select the optimal treatment, which may include medications, balloon angioplasty, coronary stenting, atherectomy ("roto-rooter"), or coronary bypass surgery. The coronary angiogram is the only test which allows the precise quantification of the extent and severity of CAD to optimally make these treatment decisions.