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Cardiac resynchronization therapy (CRT)

Learn how CRT devices can help your heart beat more efficiently and allow your doctor to monitor your health.

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Getting to know your device

Already implanted with a CRT device? Go to the device support page for more information. 

Types of CRT devices

With heart failure, your heart doesn’t pump as well as it should, so your blood fails to supply your body with the oxygen it needs. CRT devices work to help the heart pump properly in a coordinated way. There are two types of CRT devices. One is a special kind of pacemaker called a cardiac resynchronization therapy pacemaker (CRT-P) or “biventricular pacemaker.” The other is the same device but also includes a built-in implantable cardioverter defibrillator (ICD) called a cardiac resynchronization therapy defibrillator (CRT-D). 

Boston Scientific’s CRT device family

Know your device

CRT-P and CRT-D devices help your heart beat more efficiently and monitor your condition, so your doctor can provide the right treatment. A CRT device delivers tiny amounts of electrical energy to the heart. This helps restore the normal timing of the heartbeats, causing both ventricles to pump together more effectively.

Understanding the procedure

Typically, a CRT device is implanted just under the skin in your chest, near your collarbone. The leads are placed in the right atrium, the right ventricle and on the surface of the left ventricle. Your doctor will discuss with you which side of your chest the device will be implanted prior to your procedure.

Full recovery from surgery can take from several days or weeks to a few months. While you recover, your doctor may ask you to avoid strenuous activity (especially lifting and other activities that use your upper body). Doing so helps ensure the leads have time to firmly attach to your heart tissue. 

Step 1

After implantation

While you won’t feel any noticeable sensations when your CRT device is monitoring your heart, shock therapy for an arrhythmia may be very noticeable. Before you experience symptoms or receive a shock, talk to your health care team about a plan for contacting your doctor and, if necessary, emergency personnel.


  • Have a family member or friend present and available to stay with you through the event and aware to call 911 if you become unconscious
  • If you are conscious but don’t feel well after a shock, have someone call your doctor
  • If you feel fine after a shock and no more symptoms appear, it may not be necessary to seek medical help immediately. However, follow your doctor’s instructions for when to call his or her office

It’s possible that you could feel symptoms of an arrhythmia but not receive therapy. This depends on the programmed settings of your device. For example, an arrhythmia may cause symptoms, but it may not be fast enough for your device to deliver therapy. In any case, if your symptoms are severe or continue for more than a minute or so, you should seek immediate medical attention.

Step 2

During CRT

CRT-D patients report a wide range of experiences as a result of receiving a shock—from a mild thump to a kick in the chest. While the shock may be painful, it will be over in an instant. And while the sensation may be uncomfortable, it means your device is monitoring and responding to dangerous heart rhythm irregularities. The sensation you feel may vary based on the therapy your device delivers.

What to expect from defibrillation

If your arrhythmia is very irregular and fast, your device can deliver a high-energy shock to stop the arrhythmia and return your heart to its normal rhythm. Many patients faint or become unconscious shortly after a very fast ventricular tachycardia (VT) or ventricular fibrillation (VF) rhythm begins. As a result, many patients do not feel these high-energy shocks. Some say the sudden but brief sensation feels like a kick in the chest. This sensation will only last for a moment. While many find the shock reassuring, other patients may be upset for a short time after the shock is delivered.

Knowing the benefits

While functioning like a normal pacemaker, a CRT-D device delivers small electrical impulses to the left and right ventricles to treat slow heart rhythms. A CRT-D device can also treat dangerously fast heart rhythms (arrhythmias) that could lead to sudden cardiac arrest.

Explaining the risks

While complications don’t happen very often, it’s important to know that there are risks associated with the implantation of any device or lead. You should talk with your doctor about these risks, including the following:

  • Bleeding
  • Formation of a blood clot
  • Damage to adjacent structures (tendons, muscles, nerves)
  • Puncture of a lung or vein 
  • Damage to the heart (perforation or tissue damage)
  • Dangerous arrhythmias
  • Heart attack
  • Stroke 
  • Death

Some of the risks encountered after the system is implanted may include, but are not limited to, the following:

  • You may develop an infection
  • You may experience erosion of the skin near your device
  • The device may move from the original implant site
  • The lead(s) may move out of place in the heart 
  • The electrodes on the lead or the pacing pulses may cause an irritation or damaging effect on the surrounding tissues, including heart tissue and nerves
  • You may have difficulty coping with having an implanted device
  • The device might be prevented from shocking or pacing due to electromagnetic interference
  • You may receive a shock or pacing therapy when it is not needed 
  • The device might not be able to detect or appropriately treat your heart rhythms
  • The device may exhibit malfunctions that may result in lost or compromised ability to deliver therapy

See our patient manuals for detailed safety information.

Learn more about your battery

Just like any battery, the battery in your CRT-P or CRT-D will run out over time. Since the battery is permanently sealed inside your device, your entire device will need to be replaced when your battery runs out.  How long your battery lasts depends on the therapy settings and your activity level. 

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Our devices

At Boston Scientific, we are dedicated to advancing heart rhythm management technologies by creating smaller, longer-lasting implants. Download more information about your specific CRT-P or CRT-D model, including device size and longevity.

Resources for you

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Important Safety Information

Cardiac resynchronization therapy pacemakers (CRT-P) and defibrillators (CRT-D) are designed to treat heart failure patients who may or may not have symptoms or who may have symptoms despite the best available drug therapy. They are also designed to help your heart pump more effectively and meet your body’s need for blood flow.  These devices are sensitive to strong electromagnetic interference (EMI) and can be affected by certain sources of electric or magnetic fields. With all medical procedures there are risks associated.  In regard to an implanted ICD, the risks include but are not limited to inappropriate shock, lead moves out of place, loss of stimulation capability, allergic reaction, fluid underneath the skin, and infection.  In rare cases device failure or death can occur.  Be sure to talk with your doctor so that you thoroughly understand all of the risks and benefits associated with the implantation of this system.  To obtain a copy of the device Patient Handbook for more detailed device safety information, go to,  or you can request a copy by calling 1-866-484-3268 or writing to Boston Scientific, 4100 Hamline Ave. N., St. Paul, MN  55112. 

Device Quality and Reliability

It is Boston Scientific’s intent to provide implantable devices of high quality and reliability. However, these devices may exhibit malfunctions that may result in lost or compromised ability to deliver therapy. Refer to Boston Scientific’s CRM product performance report on for more information about device performance, including the types and rates of malfunctions that these devices have experienced historically. While historical data may not be predictive of future device performance, such data can provide important context for understanding the overall reliability of these types of products. Also, it is important that you talk with your doctor about the risks and benefits associated with the implantation of a device.

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