False-colour angiogram (arteriogram) of an adult human heart showing a large blockage (occlusion) in the left anterior descending (LAD) coronary artery. Coronary artery angiography is an X-ray technique in which a radio-opaque dye is injected via a catheter to outline the arteries which supply the heart. Here, the uppermost artery (top right) appears blocked for a significant part of its length; no contrast medium can penetrate the solid atheroma plaque that fills its lumen (interior). This abnormality is known as coronary artery disease & gives rise to the symptoms of chest pains called angina pectoris.