This document discusses antianginal drugs, which are used to treat or prevent angina pectoris, a type of chest pain caused by reduced blood flow to the heart. It classifies antianginal drugs into several categories, including nitrates, beta blockers, calcium channel blockers, and others. Nitrates like glyceryl trinitrate work by dilating blood vessels, reducing cardiac workload and oxygen demand. This decreases blood pressure and relieves angina by increasing oxygen supply to the heart. Nitrates are used to both abort acute angina attacks and prevent chronic episodes. Common side effects include headaches and low blood pressure.