This information is for people with heart failure. It tells you about calcium channel blockers. It is based on the best and most up-to-date research.
Do they work?
No. Most people who have heart failure do not seem to be helped by calcium channel blockers. Some of these drugs can be harmful for people with heart failure.
What are they?
Calcium channel blockers are drugs that slow down your heartbeat. They work by changing the electrical signals in your heart.
There are lots of different kinds of calcium channel blockers. They are used for many heart conditions, including high blood pressure.
Two of these drugs are not usually used in people with heart failure, because they can make it worse.  These drugs (and some common brand names) are:
diltiazem (Adrizem, Angitil, Calcicard)
verapimil (Cordilox, Univer).
Two other drugs are used with great care in people with heart failure:
Other calcium channel blockers (and their brand names) include:
These drugs tend not to be used for people with systolic heart failure, because they can make some symptoms worse. But they may help people with diastolic heart failure. Systolic means your heart can't pump hard enough. Diastolic means your heart can't relax enough to allow its chambers to fill up with blood. To learn more, see What is heart failure?
How can they help?
Calcium channel blockers don't seem to make people with heart failure feel better or help them live longer.    One study found that people whose heart failure was caused by damage to the heart muscle ( cardiomyopathy) could benefit from taking these drugs.  But in other people they could actually make heart failure worse.  
How do they work?
Calcium channel blockers help the heart to pump less strongly, so researchers thought they may help with symptoms of heart failure. But this doesn't seem to happen.
Can they be harmful?
Some calcium channel blockers can make your symptoms worse.   They can even increase your chance of dying of heart failure if you have just had a heart attack and have a lot of fluid in your lungs. The same risks apply if your heart failure is already bad and you start taking these drugs.
These drugs can also cause milder side effects, such as headaches, dizziness, and nausea. Newer calcium channel blockers (amlodipine, felodipine, isradipine, lacidipine, lercadipine, and nisoldipine) cause less serious side effects. 
How good is the research on calcium channel blockers?
There's good research that shows calcium channel blockers don't help if you have heart failure.
We found two summaries of the research on calcium channel blockers and one other good study (a randomised controlled trial).