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Home Health Library Tests and Procedures Cardiac resynchronization therapy

Cardiac resynchronization therapy


Cardiac resynchronization therapy is a procedure to implant a device in the chest to make the heart's chambers squeeze (contract) in a more organized and efficient way.

Cardiac resynchronization therapy (CRT) uses a device called a biventricular pacemaker — also called a cardiac resynchronization device — that sends electrical signals to both lower chambers of the heart (right and left ventricles). The signals trigger the ventricles to contract in a more coordinated way, which improves the pumping of blood out of the heart.

Sometimes the device also contains an implantable cardioverter-defibrillator (ICD), which can deliver an electrical shock to reset the heartbeat if the heart rhythm becomes dangerously irregular.

Why it's done

Cardiac resynchronization therapy is a treatment for heart failure in people whose lower heart chambers (ventricles) don't contract in a coordinated fashion. It's frequently used for people who have heart failure and a condition called left bundle branch block or for people who are likely to require cardiac pacing due to low heart rates.

If you have heart failure, your heart muscle is weakened and may not be able to pump out enough blood to support your body. This can be worsened if your heart's chambers aren't in sync with each other.

Cardiac resynchronization therapy may reduce symptoms of heart failure and lower the risk of heart failure complications, including death.


All medical procedures come with some type of risk. The specific risks of cardiac resynchronization therapy depend on the type of implant and your overall health.

Complications related to cardiac resynchronization therapy and the implantation procedure may include:

  • Infection
  • Bleeding
  • Collapsed lung (pneumothorax)
  • Compression of the heart due to fluid buildup in the sac surrounding the heart (cardiac tamponade)
  • Failure of the device
  • Shifting of device parts, which could require another procedure

What you can expect

Cardiac resynchronization therapy requires a minor surgical procedure to implant a device in the chest.

You'll likely be awake during the procedure, but will receive medication to help you relax. The area where the pacemaker is implanted is numbed. The procedure typically takes a few hours.

During surgery, insulated wires (leads, also called electrodes) are inserted into a major vein under or near the collarbone and move to the heart using X-ray images as a guide. One end of each wire is attached to the appropriate position in the heart. The other end is attached to a pulse generator, which is usually implanted under the skin beneath the collarbone.

Cardiac resynchronization therapy devices include:

  • Cardiac resynchronization therapy with a pacemaker (CRT-P). The device used for cardiac resynchronization therapy has three leads that connect the pacemaker to the right upper chamber of the heart (right atria) and both lower chambers (ventricles).
  • Cardiac resynchronization therapy with a pacemaker and an ICD (CRT-D). This device may be recommended for people with heart failure who also have a risk of sudden cardiac death. It can detect dangerous heart rhythms and deliver a stronger shock of energy than a pacemaker can deliver. This shock can reset the heartbeat.

You'll usually stay overnight in the hospital after cardiac resynchronization therapy. Your health care provider will test your device to make sure it's programmed correctly before you leave the hospital. Most people can return to their usual activities after a few days, although driving and heavy lifting might be restricted for a time.

Last Updated: March 16th, 2022