This information is for people who have unstable angina. It tells you about calcium channel 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. These drugs may not reduce your risk of having a heart attack or dying if you have unstable angina. But doctors often give them to relieve chest pain.
What are they?
Calcium channel blockers are drugs that are used to treat other heart problems, such as irregular heartbeats. They disrupt the electrical activity in your heart and blood vessels. Heart muscle cells, like nerve cells, are driven by electrical activity. By interfering with this, calcium channel blockers can:
They can also:
There are two kinds of calcium channel blockers: those that work mainly on arteries to lower your blood pressure and those that work mainly on your heart.
Some common calcium channel blockers (and their brand names) are listed below.
diltiazem (Adizem, Dilzem, Tildiem)
nifedipine (Adalat, Coracten SR)
verapamil (Cordilox, Univer)
People usually take these drugs as tablets.
How can they help?
We don't know whether these drugs can help if you have unstable angina. So far, studies show that they probably won't reduce your chances of having a heart attack or dying. 
One study also found they don't work as well as drugs called beta-blockers at reducing chest pain in the 48 hours after an attack of unstable angina, or at reducing the risk of a heart attack. 
How do they work?
When calcium gets into heart cells, it makes them want to pump. By stopping this process, calcium channel blockers can make your heart pump more gently.
Doctors thought calcium channel blockers might work for people with unstable angina because these drugs have the same kinds of actions as other drugs that seem to help. For example, they can slow your heart down and make it less excitable. And, like beta-blockers, they can lower your blood pressure.
All of these actions stop your heart working too hard, so they should protect it. But these drugs don't seem work as well as beta-blockers for people with unstable angina. 
Doctors still use calcium channel blockers sometimes as well as beta-blockers or nitrates.  Your doctor might also give you a calcium channel blocker if you can't take a beta-blocker.
Can they be harmful?
Studies show that some calcium channel blockers, such as nifedipine, are harmful and may increase the risk of dying in people who have narrowed arteries in their heart (coronary artery disease).   Many people with unstable angina have this disease. So doctors are very careful about using these drugs.
These drugs can also cause other side effects that are less serious. For example, you may get headaches, feel dizzy, or feel sick.