Pacemakers are implanted to help control your heartbeat. They can be implanted temporarily to treat a slow heartbeat after a heart attack, surgery or overdose of medication. Pacemakers can also be implanted permanently to correct a slow heartbeat (bradycardia) or, in some cases, to help treat heart failure. To understand how a pacemaker works, it helps to know how your heart beats.

How your heart beats

The heart is a muscular, fist-sized pump with four chambers, two on the left side and two on the right. The upper chambers are the right and left atria. The lower chambers are the right and left ventricles.

For your heart to function properly, the heart's chambers must work in a coordinated fashion. Your heart must also beat at an appropriate rate — normally from 60 to 90 beats a minute in resting adults. If your heart beats too slowly or too rapidly, not enough blood flows through your body, leading to fatigue, fainting, shortness of breath, confusion, and other signs and symptoms.

Your heart's electrical system controls the chambers' pumping action. A normal heartbeat begins in your right atrium, in the sinus node. This cluster of cells — your natural pacemaker — acts like a spark plug, generating regular electrical impulses that travel through specialized muscle fibers.

When an electrical impulse reaches both the right and left atria, they contract and squeeze blood into the ventricles. After a split-second delay to allow the ventricles to fill, the impulse reaches the ventricles, making them contract and pump blood to the rest of your body.

What a pacemaker does

An implanted electronic pacemaker mimics the action of your natural pacemaker. An implanted pacemaker consists of two parts:

• The pulse generator. This small metal container houses a battery and the electrical circuitry that regulates the rate of electrical pulses sent to your heart.
• Leads (electrodes). One to three flexible, insulated wires are each placed in a chamber, or chambers, of your heart and deliver the electrical pulses to adjust your heart rate.

Pacemakers monitor your heartbeat and, if it's too slow, the pacemaker will speed up your heart rate by sending electrical signals to your heart. In addition, most pacemakers have sensors that detect body motion or breathing rate, which signals the pacemaker to increase your heart rate during exercise to meet your body's increased need for blood and oxygen.

Single-chamber pacemakers

These types of pacemakers usually carry electrical impulses from the pulse generator to the right ventricle of your heart.

Dual-chamber pacemakers

Dual-chamber pacemakers carry electrical impulses from the pulse generator to both the right ventricle and the right atrium of your heart. The impulses help control the timing of contractions between the two chambers.

Biventricular pacemakers

Biventricular pacemakers are a treatment option for people with heart failure whose hearts' electrical systems have been damaged. Unlike a regular pacemaker, a biventricular pacemaker stimulates both of the lower chambers of your heart (the right and left ventricles) to make the heart beat more efficiently. A biventricular pacemaker paces both ventricles so that all or most of the ventricular muscle pumps together. This allows your heart to pump blood more effectively. Because this treatment resets the ventricles' pumping mechanism, it's also referred to as cardiac resynchronization therapy (CRT).

Complications from having surgery to implant your pacemaker are uncommon, but could include:

• Infection where the pacemaker was implanted
• Allergic reaction to the dye or anesthesia used during your procedure
• Swelling, bruising or bleeding at the generator site, especially if you are taking blood thinners
• Damage to your blood vessels or nerves near the pacemaker
• Collapsed lung
• Puncture of your heart muscle, which can lead to bleeding into the lining (pericardium) of your heart and may require emergency medical care

Life-threatening complications of pacemaker implantation are rare.

Before your doctor decides if you need a pacemaker, you'll have several tests done to find out the cause of your irregular heartbeat. These could include:

• Electrocardiogram. In this noninvasive test, sensor pads with wires attached, called electrodes, are placed on your chest and sometimes limbs to measure your heart's electrical impulses. Your heart's beating pattern can offer clues to the type of irregular heartbeat you have.
• Holter monitoring. Also known as an ambulatory electrocardiogram monitor, a Holter monitor records your heart rhythms for an entire 24-hour period. Wires from electrodes on your chest go to a battery-operated recording device carried in your pocket or worn on a belt or shoulder strap. While you're wearing the monitor, you'll keep a diary of your activities and symptoms. Your doctor will compare the diary with the electrical recordings to try to figure out the cause of your symptoms.
• Echocardiogram. This noninvasive test uses harmless sound waves that allow your doctor to see your heart without making an incision. During the procedure, a small, plastic instrument called a transducer is placed on your chest. It collects reflected sound waves (echoes) from your heart and transmits them to a machine that uses the sound wave patterns to compose images of your beating heart on a monitor. These images show how well your heart is functioning, and recorded pictures allow your doctor to measure the size and thickness of your heart muscle.
• Stress test. Some heart problems occur only during exercise. For a stress test, an echocardiogram or electrocardiogram is taken before and immediately after walking on a treadmill or riding a stationary bike. Other types of treadmill exercise tests also can be done to evaluate your heart, including an oxygen consumption test that measures how much oxygen your body is using.

During the procedure

Surgery to implant the pacemaker is usually performed while you're awake and typically takes a few hours. You'll be given a sedative to relax, and the area where your pacemaker is inserted will be numbed.

During surgery, one or more flexible, insulated wires (leads or electrodes) are inserted into a major vein under or near your collarbone and guided to your heart with the help of X-ray images. One end of each wire is secured to the appropriate position in your heart, while the other end is attached to the pulse generator, which is usually implanted under the skin beneath your collarbone.

After the procedure

You'll usually stay in the hospital for one day after having a pacemaker implanted. Before you leave, your pacemaker is programmed to fit your particular pacing needs. A return visit is often scheduled to make sure your pacemaker's settings are correct.

After that, most pacemakers can be checked remotely using wireless technology. Using your cellphone or radiofrequency signals, your pacemaker transmits and receives information between you and your doctor's office, where your doctor can access the data — including your heart rate and rhythm, how your pacemaker is functioning, and remaining battery life. Remote transmissions can be made at scheduled intervals or at unscheduled times if your pacemaker sends an alert, or you can send a transmission if you have a concern. Remote technology means fewer trips to the doctor's office, but you'll still need to be seen by your doctor in person for scheduled checkups.

After your procedure to implant your pacemaker, your doctor may recommend that you avoid vigorous exercise or heavy lifting for about a month. You may have some aches and pains near the area where your pacemaker was implanted. These pains can be relieved with over-the-counter medicines, such as acetaminophen (Tylenol, others) or ibuprofen (Motrin IB, Advil, others), but talk to your doctor before taking any pain relievers.

Special precautions

It's unlikely that your pacemaker would stop working properly because of electrical interference. Still, you'll need to take a few precautions:

• Cellphones. It's safe to talk on a cellphone, but avoid placing your cell phone directly over your pacemaker implantation site when the phone is turned on. Although unlikely, your pacemaker could misinterpret the cellphone signal as a heartbeat and withhold pacing, producing symptoms, such as sudden fatigue.
• Security systems. Passing through an airport metal detector won't interfere with your pacemaker, although the metal in it may sound the alarm. But avoid lingering near or leaning against a metal-detection system. If security personnel insist on using a hand-held metal detector, ask them not to hold the device near your pacemaker any longer than necessary or ask for an alternative form of personal search. To avoid potential problems, carry an ID card stating that you have a pacemaker.
• Medical equipment. If a doctor is considering any medical procedure that involves intensive exposure to electromagnetic energy, tell him or her that you have a pacemaker. Such procedures include magnetic resonance imaging, therapeutic radiation for cancer treatment and shock wave lithotripsy, which uses shock waves to break up large kidney stones or gallstones. If you're having surgery, a procedure to control bleeding (electrocautery) also can interfere with pacemaker function.
• Power-generating equipment. Stand at least 2 feet (60 centimeters) from welding equipment, high-voltage transformers or motor-generator systems. If you work around such equipment, your doctor can arrange a test in your workplace to determine whether it affects your pacemaker.

Devices that are unlikely to interfere with your pacemaker include microwave ovens, televisions and remote controls, radios, toasters, electric blankets, electric shavers, and electric drills.

Once your pacemaker is implanted, the battery should last five to 10 years, which is the average battery life. When a pacemaker's battery wears out, the entire pacemaker's pulse generator is replaced, and you'll need another procedure to fix your device. The leads of your pacemaker can be left in place — though they may need to be replaced eventually — and the procedure to change your pacemaker's battery is often quicker and requires less recovery time than the procedure to first implant your pacemaker.

Pacemakers are a standard treatment for many conditions affecting your heart's electrical system. By preventing a slow heart rate, pacemakers can treat symptoms, such as fatigue, lightheadedness and fainting. Because most of today's pacemakers automatically adjust your heart rate to match your level of physical activity, they can allow you to resume a more active lifestyle.

Pacemakers and end-of-life issues

If you have a pacemaker and become terminally ill with a condition unrelated to your heart, such as cancer, it's possible that your pacemaker could prolong the process of dying. Doctors and researchers have varied opinions on turning off a pacemaker in end-of-life situations.

If you have a pacemaker and are concerned about turning it off, talk to your doctor. You may also want to talk to family members or another person designated to make medical decisions for you about what you'd like to do in end-of-life care situations.