Arformoterol is used as a long-term (maintenance) treatment to prevent and decrease wheezing and shortness of breath caused by breathing problems (such as chronic obstructive pulmonary disease, including chronic bronchitis and emphysema). Arformoterol belongs to the class of drugs known as long-acting beta agonists (LABAs). Arformoterol is also known as a bronchodilator. It works by relaxing the muscles around the airways so that they open up and you can breathe more easily. Controlling symptoms of breathing problems can decrease time lost from work or school. This medication does not work right away and should not be used for sudden attacks of breathing trouble. Your doctor must prescribe a quick-relief medicine/inhaler (such as albuterol, also known as salbutamol) for sudden shortness of breath while you are using arformoterol. You should always have a quick-relief inhaler with you. Arformoterol is not approved to treat asthma. People with asthma using long-acting inhaled beta agonists (such as arformoterol) without also using an inhaled corticosteroid may have an increased risk of serious (sometimes fatal) breathing problems.