An older woman who is experiencing angina is shown. Her thoracic anatomy is revealed, and her angiogram is then exhibited. Angina is chest pain experienced because of oxygen-deficient blood flowing into the heart. Angina is a symptom of a circulatory condition. In this case it is ischemia (also known as coronary heart disease), which occurs when plaque build-up narrows the artery. This narrowing of the blood vessel restricts blood flow and oxygen within the circulatory system. Part of an artery shown on this woman's angiogram (circled in white) becomes less visible. This invisible space represents lack of blood flow and blood clotting within the artery, caused by an embolus (a piece of plaque or blood clot) that is lodged inside the arterial walls.