A cardiologist in a sterile operating theatre environment performs this test.

You will be asked not to eat or drink after midnight the evening before the procedure.
You are not given a general anesthetic but may have some medication to relax you if needed. Local anesthetic is injected into an area of skin to the side of your groin or in your arm.  A needle and then tube are fed into an artery here and advanced though the blood vessels to the heart. You can’t feel this. Dye is then injected so that the heart and blood vessels can be seen on X-ray.  X-rays and measurements are then taken giving the doctors information about the state of your heart and the exact nature of any narrowed blood vessels.  This allows them to plan the best form of treatment to prevent heart attacks and control any symptoms you may have.

After the procedure you will have to lay flat for several hours to prevent bleeding.