Metoprolol tartrate is a selective beta1-adrenoreceptor blocking agent.  It can treat high blood pressure, chest pain (angina), and heart failure. This may lower the risk of death after a heart attack.  It is also used to prevent further heart problems after myocardial infarction and to prevent headaches in those with migraines. 

Common side effects include trouble sleeping, feeling tired, feeling faint, and abdominal discomfort.  Metoprolol was first made in 1969.  It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.  In 2013, metoprolol was the 19th-most prescribed medication in the Unisted States.