Cardiac catheterization is a procedure in which a doctor guides a thin plastic tube called a catheter through an artery or vein in the leg (or rarely from the arm) and into the heart to allow pressure measurements, blood sampling, and angiograms to allow visualization of the coronary arteries and chambers of the heart. Rarely a sample or biopsy of heart tissue can be taken during the procedure. At other times the heart’s rhythm can be assessed.
Coronary angiography involves using x-rays to record the passage of a contrast dye in the heart. Angiography enables doctors to see any problems in blood flow in the coronary arteries, such as atherosclerosis (“hardening of the arteries”), regurgitation or pooling of blood in a chamber because of a valve malfunction.
This information is helpful in establishing the cause of symptoms, the extent of disease, and the need and feasibility of angioplasty, bypass, and other procedures.
You can find further information here: The American Heart Association Website