Chemical compounds that have a valuable role in the treatment of ANGINA PECTORIS. They are very effective in dilating the ARTERIES supplying the HEART; their prime benefit, however, is to reduce the return of venous blood to the heart, thus reducing the demands on the left ventricle, which pumps deoxygenated blood to the lungs. Undesirable side-effects such as flushing, headache and postural HYPOTENSION may restrict the use of nitrates. Among the nitrate drugs used is GLYCERYL TRINITRATE which, taken under the tongue (sublingually), provides quick, symptomatic relief of angina, lasting for up to half an hour. Alternative administration can be via a spray product. Isorbide dinitrate taken sublingually is a more stable preparation, suitable for patients who need nitrates infrequently. The drug's effect may last for 12 hours in modified-release form. Patients taking long-acting nitrates or preparations absorbed through the skin (transdermal) may develop TOLERANCE.