This information is for people with heart failure. It tells you about pacemakers, which are devices used for heart failure. It is based on the best and most up-to-date research.
Does it work?
Yes. If you have heart failure, you may be able to have a pacemaker fitted to make the left and right sides of your heart beat together. This can help you be more active. It may also help you stay out of hospital and live longer.
What is it?
A pacemaker is an electrical device that's put in your chest. It's used to treat an abnormal heartbeat. You'll have an operation to put the pacemaker under the skin in your chest, just under your collarbone.
The main part of a pacemaker is roughly the size of a pack of cards. It weighs about 25 grams (less than an ounce). It contains a battery and wires that run from the pacemaker to your heart. Electric pulses travel down the wires and make your heart beat in a steady rhythm.
Normally, the left and right sides of your heart beat together. But if you have heart failure, the two sides of your heart may beat a fraction of a second apart.  If this happens, your heart doesn't pump as strongly as it should.
There are different types of pacemakers. They have one, two, or three wires. The wires are attached to different parts of the heart, depending on the type of problem you have.
In this section we deal with a type of pacemaker called a cardiac resychronisation therapy pacemaker. This pacemaker had three wires. Two of the wires run to the upper and lower chamber on the right side of your heart. The third wire runs to the lower chamber on the left side of your heart. The electrical signals from the pacemaker make both sides of your heart beat together.
You may hear this treatment called cardiac resynchronisation therapy, or CRT. The pacemaker itself may be called a CRT device or a cardiac resynchronisation implant.
This type of pacemaker is sometimes combined with a device that can shock your heart into starting again if it stops beating. This is called a defibrillator. To read more, see Having a defibrillator put in. This combination of a pacemaker and defibrillator is sometimes called a CRT-D device.
How can it help?
Having a pacemaker put in to make the two sides of your heart beat together can help you:  
Most of the studies of this treatment looked at people who had severe heart failure. Their condition was rated as class III or class IV on a scale that's used to say how bad heart failure is. (To read more, see How heart failure is classified.) But we did find studies that showed this treatment also helped people with less severe heart failure.