False-colour coronary angiogram of a normal healthy heart. Angiography is the X-ray examination of arteries after they have been outlined by prior injection of a radio-opaque contrast medium. Here, the branches of the main left and right coronary arteries appear as the network of yellow ribbons across the heart. Coronary angiography is used to assess the presence or extent of arterial disease, where the major arterial branches may become obstructed through the formation of atheroma plaques. A clot or embolus lodging in such a restricted artery might cause total blockage & the death of a section of heart muscle - myocardial infarction.