Isosorbide dinitrate belongs to the group of medicines called nitrates. It works by relaxing the blood vessels and increasing the supply of blood and oxygen to the heart while reducing its work load. When used regularly on a long-term basis, this helps prevent angina attacks from occurring. Isosorbide is in a class of medications called vasodilators. It works by relaxing the blood vessels so the heart does not need to work as hard and therefore does not need as much oxygen.