Pacemakers How They Work

Pacemakers use low-energy electrical pulses to control the rate and rhythm of your heartbeat. Traditional pacemakers send the electrical pulses through wires, also known as leads. Wireless pacemakers are a newer kind of pacemaker without wires. 

Learn more about your heart’s electrical system in our How the Heart Works Health Topic.

Traditional transvenous pacemakers

Traditional pacemakers (also called transvenous pacemakers) have three main parts. 

  • A pulse generator creates the electrical pulses. 
  • Wires (also called leads) are implanted inside the veins and carry the pulses to your heart. 
  • Electrodes sense your natural heartbeat. When your heartbeat is slower than normal, the electrodes deliver electrical impulses to your heart to make it beat normally. 

The device can send data to your doctor remotely. Your doctor will use these recordings to set up your pacemaker so it works better for you.

cross section of a pacemaker
The image shows a cross-section of a chest and heart with a traditional pacemaker, which has wires (leads). Figure A shows a double-lead pacemaker (also called a double-chamber pacemaker) in the upper chest. Figure B shows an electrode using electrical signals to activate the heart muscle. Figure C shows a single lead pacemaker (also called a single-chamber pacemaker) in the upper chest. Wireless pacemakers (not pictured) are placed inside the right ventricle.


A traditional pacemaker generator is placed outside of your heart, either in your chest or abdomen. It is connected via wires to electrodes inside one to three heart chambers. 

Single- and double-lead pacemakers send pulses to the right side of the heart. A biventricular pacemaker sends pulses to both ventricles and an atrium. The pulses help coordinate electrical signaling between the two ventricles to help your heart pump blood. This type of pacemaker is also called a cardiac resynchronization therapy (CRT) device. 

Wireless pacemakers

Wireless, or leadless, pacemakers are smaller than traditional types (about the size of a large pill capsule). The pulse generator and electrodes are all in one device that is placed inside a chamber of your heart through a small tube inserted in one of your veins. No surgery is needed. Once in place, the pacemaker then sends pulses to the right ventricle. 

Your doctor may recommend a wireless pacemaker if you have a slow heartbeat, or if you have an electrical block, which is when the flow of electricity to the heart is delayed between the upper and lower chambers of your heart. Depending on the type, this kind of pacemaker may sense the right atrium (upper chamber), which allows it to match the signals that it sends to the ventricle. This helps the two chambers beat in sync.

Other types of pacemakers

In another type of pacemaker, the electrodes are placed on the surface of your heart rather than inside your heart. This type of pacemaker requires surgery. 

Learn more about the different types of pacemakers in What to Expect

Doctors also treat life threatening arrhythmias with a similar device called an implantable cardioverter defibrillator (ICD). The device constantly tracks your heart rate. If your heart shows an irregular and very fast rhythm, the ICD delivers an electric shock to reset your heart rhythm to prevent sudden cardiac arrest. Visit our Defibrillators Health Topic to learn more.

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