An isosorbide mononitrate tablet is a nitrate that dilates (widens) blood vessels, making it easier for blood to flow through them and easier for the heart to pump. Isosorbide mononitrate is used to prevent angina (chest pain) caused by coronary artery disease (heart disease). It does not work fast enough to relieve the pain of an angina attack that has already started. Isosorbide Mononitrate Tablet works by relaxing the blood vessels and increasing the supply of blood and oxygen to the heart while reducing its workload.