This information is for people who have unstable angina. It tells you about beta-blockers, a treatment used for unstable angina. It is based on the best and most up-to-date research.
Do they work?
We don't know. If you take a beta-blocker, you may have less chest pain in the first few days after your attack of unstable angina. And the pain may be milder. But we are not sure if these medicines lower your risk of having a heart attack or of dying.
Still, doctors tend to use beta-blockers for unstable angina. This is partly because of the way these medicines work on your heart, and partly because doctors know that these medicines help people who have had a heart attack or have the stable kind of angina. 
What are they?
Beta-blockers are a group of drugs that are used to treat heart problems. Doctors prescribe them for unstable angina to lower the chance of damage to the heart muscle. They slow your heart down. And they reduce the amount of work your heart needs to do. This means your heart doesn't need as much oxygen. Your doctor will advise you about how long to keep taking beta-blockers.
Here are some common beta-blockers (and their brand names).
Some beta-blockers can be injected straight into your bloodstream. Others come as tablets. Doctors may give you the injected kind in the first few hours after an attack of unstable angina. This is because injections work faster than tablets.
How can they help?
We don't know if these drugs can reduce your risk of having a heart attack or of dying. But we do know that if you have a beta-blocker to treat your unstable angina, you will have less chest pain in the first few days after your attack.  
Even if you are already taking other drugs, such as a nitrate drug or a calcium channel blocker, you may get less chest pain if you take a beta-blocker as well. 
One study found that the beta-blocker metoprolol may work better than a calcium channel blocker called nifedipine at reducing your chance of getting more chest pain or having a heart attack in the two days after an attack of unstable angina. 
How do they work?
Beta-blockers stop the action of chemicals called adrenaline and noradrenaline. Your body makes these chemicals when you are scared, angry, or in pain. They increase your blood pressure. And they make your heart race and beat more forcefully. The pain and anxiety you feel when you have unstable angina cause your body to make adrenaline and noradrenaline.
Beta-blockers reduce the effects of these chemicals on your heart. So they slow your heart down and stop it working too hard. A slower, more relaxed heart uses less oxygen. And that's important if the vessels that carry blood to your heart (your coronary arteries) are narrower than normal because of a blood clot. Your heart gets oxygen from your blood. When your heart needs less oxygen, the pain from your unstable angina eases off.
Because they stop your heart working too hard, beta-blockers do some other good things.
They lower your blood pressure and stop it rising suddenly when you feel anxious, under stress, or in pain. This can help prevent a heart attack.
They help control your heartbeat so you have less chance of getting a fast, abnormal heartbeat (called arrhythmia).