Metoprolol tartrate (Prolomet-R) tartrate is a beta-adrenergic blocking agent (beta-blocker). It works by reducing the amount of work the heart has to do (reduces chest pain) and the amount of blood the heart pumps out (lowers high blood pressure). It is also used to stabilize the heart rhythm in conditions in which the heart is beating too fast or in an irregular rhythm. Treating high blood pressure, alone or with other medicines; long-term treatment of chest pain; and reducing the risk of death because of heart problems in patients who have had a heart attack. It may also be used for other conditions as determined by your doctor.