Cardiac Catheterization Cardiac catheterization is an x-ray test that uses injection of radiographic dye (contrast) via a thin catheter inserted in the large arteries or veins in the upper thigh. Pictures are taken of the structures of the heart and measurements of pressures and oxygen levels within the heart chambers and veins and arteries are made. Interventional procedures include balloon dilation of narrowed heart valves (balloon valvuloplasty), balloon dilation of narrowed arteries or veins (balloon angioplasty) and insertion of stents that "prop open" narrowed blood vessels. Finally, interventional procedures are available for the closure of holes in the heart (occluder) and abnormal blood vessels (coils).