The most common cause of angina is the build up of atheroma , composed of cholesterol and other lipids, in larger coronary arteries. The obstruction to blood flow may become so severe that not enough blood can pass through the arteries to supply the myocardium when oxygen demand increases, for example during exercise. The ischaemic muscle produces the characteristic symptoms of angina pectoris , probably because metabolites produced by myocardial contraction accumulate in the poorly perfused tissue. These symptoms include retrosternal chest pain or tightness, which often radiates to the arms. The pain is usually caused or increased by exercise, and relieved by rest and treatment with nitrates.
Nitrates are the drugs of first choice.
This reduction in distension of the heart wall decreases oxygen demand and the pain of angina is relieved quickly. At the same time nitrates improve myocardial oxygen supply by increasing the coronary blood flow to the endocardium. Cardiac output is usually unchanged or decreased slightly, and a reflex tachycardia occurs in normal subjects. However in patients with heart failure, who have a high systemic vascular resistance, cardiac output may increase and there is little change in the heart rate. It is more useful in preventing attacks of angina than in stopping them once they have begun.