Coronary artery disease before angioplasty. Colour angiogram of the heart showing stenosis (obstruction) in the circumflex coronary artery, one of the arteries that supply the heart with blood. The stenosed section appears as the narrowed section immediately above the inverted U-shaped artery in centre. Healthy arteries appear as continuous, even, purple-coloured ribbons. Atherosclerosis (narrowing of arteries) most commonly occurs near the bifurcation (division) of arteries, as seen in this image. Blood flow within an affected artery is greatly reduced, provoking the symptoms of angina. A total block results in myocardial infarction, a heart attack.