Heart block is a disruption in the electrical signals that control your heart.

Your heart depends on a steady flow of electrical signals that start in the heart’s upper chambers (atria). The signals then travel down the lower heart chambers (ventricles), triggering the ventricles to pump blood out of the heart into the lungs and to the rest of the body. Heart block occurs when there’s an interference with this electrical activity between the atria and ventricles.

A heart block is often the result of a heart attack or other injury to the heart, but it can have other causes. If the heart block is minor, treatment may not be necessary. If it’s more severe, a pacemaker may be needed to restore healthy electrical activity in the heart.

Read on to learn about the types of heart block, causes, symptoms to watch out for, and common treatments.

A heart block, also known as an atrioventricular (AV) block, is classified by degree, based on how severe the electrical blockage is between the upper and lower heart chambers.

First degree

In first-degree heart block, electrical signals slow as they move from the upper chambers to the lower chambers of the heart. However, the signals don’t stop, even intermittently.

First-degree heart block is more common in adults over the age of 60, affecting an estimated 6% of that population. The prevalence of first-degree heart block in people under age 60 is 1% to 1.5%.

Second degree

Second-degree heart block is categorized in two ways: Type I and Type II.

  • Type I: This is also called Mobitz Type I or Wenckebach’s AV block. It’s a less severe form of second-degree heart block and is characterized by gradually slower electrical activity to the point where the heart skips a beat.
  • Type II: Also known as Mobitz Type II, this occurs when an increasing number of electrical signals fail to reach the ventricles. This causes a slower, abnormal rhythm. Type II is most often associated with structural heart diseases, such as myocardial fibrosis, a condition that involves the thickening of heart muscle tissue that’s triggered by hypertension or heart disease.

Third degree

Third-degree heart block is more severe than the other types. It means that the electrical signal from the atria is completely blocked from reaching the ventricles.

As a result, the ventricles often begin to beat on their own. The heartbeat is much slower and more irregular, making it hard for the heart to pump enough blood to meet the body’s demands. It can result in a very slow pulse or no pulse at all.

Third-degree heart block is rare, affecting less than 0.05% of the population.

Heart block is usually the result of a trauma that affects the heart’s electrical system. Your risk of heart block also increases as you get older. Other risk factors include a history of:

Several medical conditions may also increase the risk of heart block, including:

A 2019 study also suggests that two key cardiovascular risk factors — high blood pressure and elevated blood glucose levels — are associated with higher risks of developing heart block.

Open-heart surgery may also raise the risk of heart block or other heart rhythm disturbances (arrhythmias).

Additionally, heart block can be a side effect of some types of drugs. Medications associated with heart block include:

Although rare, heart block can also be a congenital condition, affecting an estimated 1 out of 15,000 to 22,000 live births. In most congenital heart block cases, the mother had an autoimmune disorder, such as lupus or Sjögren’s syndrome.

The type and severity of symptoms depends on the type of heart block.

First-degree symptoms

Many times, first-degree heart block has no symptoms. An abnormal heart rate and rhythm may be detected during a routine electrocardiogram (ECG).

Second-degree symptoms

When symptoms are present in second-degree heart block, they usually include fatigue and lightheadedness, sometimes resulting in fainting (syncope). Other possible symptoms of second-degree heart block include:

  • chest pain
  • heart palpitations (feeling as though the heart is skipping a beat)
  • nausea
  • shallow or rapid breathing

Third-degree symptoms

Symptoms caused by third-degree heart block are usually more severe and are considered a medical emergency. The most common symptoms include:

Heart block is not always serious, but it depends on the type. First-degree and even second-degree heart block (Type I), may be managed with little or no treatment. These types of heart block may have little impact on your long-term health or quality of life.

Second-degree (Type II) and third-degree heart block usually need a pacemaker, but with certain lifestyle changes, you may be able to live comfortably for a long time. In rare cases, patients that experience frequent fainting episodes (syncope) due to heart block may also require a pacemaker.

One of the most serious risks of heart block is heart failure. A 2018 study suggests that in cases of complete heart block, there is a significantly higher risk of heart failure. Third-degree heart block can also cause damage to internal organs and cardiac arrest (no heartbeat).

A comprehensive evaluation of your heart health should include a physical exam in which your doctor listens to your heart with a stethoscope. They should also review your personal and family medical history, medications and supplements you’re taking, and your symptoms.

First-degree heart block, and some cases of second-degree heart block, are often detected through a routine physical exam and ECG. An ECG is a noninvasive test that uses electrodes to measure your heart’s rhythm, rate, and strength, as well as the pattern of your heart’s electrical activity.

For intermittent electrical abnormalities, you may be advised to wear a portable ECG monitor, such as a Holter monitor, for 24 hours or more.

In rare cases, your doctor may also order an electrophysiology study, which involves placing a catheter into a blood vessel. The catheter is then guided to the heart to monitor the heart’s electrical activity.

Most cases of first-degree heart block don’t require any treatment. However, with some types of second-degree heart block as well as third-degree heart block, a pacemaker is usually necessary.

A pacemaker is a small battery-powered device surgically implanted in the chest. It senses when the heart is beating abnormally and sends mild electrical charges to the heart to restore a healthy heartbeat.

A study of pacemakers to treat heart block suggests that both dual-chamber pacing (which involves sending signals to both the upper and lower heart chambers) and synchronous ventricular pacing (which only stimulates the lower chamber) are both effective long-term solutions for heart block. However, having heart failure or other serious medical conditions can affect long-term effectiveness.

Heart block can’t always be prevented. Because it’s often a complication of heart disease, the best way of lowering your risk is to follow a heart-healthy lifestyle that includes:

  • eating a heart-healthy diet, such as the Mediterranean diet
  • exercising regularly, aiming for at least 150 minutes a week of moderate-intensity aerobic activity
  • not smoking
  • managing your weight
  • managing stress in a healthy way, including getting 7 to 9 hours of sleep each night
  • getting regular check-ups with your doctor

Heart block is the disruption of the electrical energy flow from your heart’s upper chambers (atria) to the lower chambers (ventricles). If it’s a minor disruption, you may not need treatment. However, if the heart block is more severe, you may need a pacemaker to maintain healthy heart function.

While heart block can’t always be prevented — age and heart disease are the most common risk factors — a heart-healthy lifestyle that reduces the risk of heart attack and cardiovascular disease may help lower the odds of developing this condition.