Atenolol is used alone or in combination with other medications to treat high blood pressure. It also is used to prevent angina (chest pain) and treat heart attacks. Atenolol is in a class of medications called beta blockers. It works by slowing the heart rate and relaxing the blood vessels so the heart does not have to pump as hard. Tenormin / Atenolol belongs to the group of medicines known as beta-blockers. You are likely to have been prescribed it because you have high blood pressure, or angina chest pain, or an uneven heartbeat. Atenolol slows down the activity of your heart by stopping messages sent by some nerves to your heart. It does this by blocking tiny areas (called beta-adrenergic receptors) where the messages are received by your heart. As a result, your heart beats more slowly and with less force. This allows the pressure of blood within your blood vessels to be reduced if you have hypertension (high blood pressure), and helps to prevent abnormally fast heart rhythms, or arrhythmias. Because your heart is using less energy, this also helps to reduce chest pain if you have angina. Atenolol may be prescribed to help prevent migraine. The leaflet does not contain information about this use of atenolol. If you have been given it for this reason, ask your doctor if you have any questions about your treatment.