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Top 6 Causes of Slow Heart Rate

How to tell when a slow heart rate is normal and when it may be a sign of a serious problem.
An illustration of a dark blue heart with a medium blue indicator like on a blood pressure dial. An arch is over the heart with a gradient of white to blue from left to right.
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Written by Jay Patel, MD.
UCLA Health Cardiology Fellow
Last updated April 8, 2024

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4 most common cause(s)

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Causes of a slow heart rate

It’s normal for your heart rate to change throughout the day. It speeds up when you exercise, slows down as you recover from exercising, and is usually at its lowest while you sleep.

Sometimes people have a slower heart rate than normal. This is called bradycardia, and it isn’t necessarily a problem. It’s diagnosed when your heart beats less than 60 beats per minute.

There are several causes of a slow heart rate. The most common are being young or physically fit. The heart is a muscle, and just like the other muscles in your body, it responds positively to exercise. When you’re in good shape, your heart doesn’t need to beat as often to supply your body with enough oxygen.

But a slow heart rate can also be a sign of a medical problem, such as a heart condition. If your resting heart rate is slow and you have other symptoms of bradycardia such as lightheadedness, call your doctor or go to the ER.


1. Conduction system disease


  • Slow heart rate
  • Lightheadedness
  • Dizziness
  • Weakness
  • Loss of consciousness

Conduction system disease occurs when there’s a problem with the electrical system that makes your heart beat. Your heart beats when an electrical signal that starts at the top of the heart travels to the bottom of the heart.

Conduction system disease can develop as you get older. With more wear-and-tear on your body, the electrical “wiring” that controls your heartbeat may fray. This leads to a slowing, or in some cases a complete break, of the signal that makes your heart beat.

If conduction system disease is significant and interferes with your everyday functioning, see your doctor as soon as possible. You may need to get a pacemaker to help restore your normal heart rate.

Pro Tip

The most important question to ask about a slow heart rate is, “What is the cause?” Since there are several, each of which has a different treatment approach, it is crucial to identify the underlying disease process. —Dr. Jay Patel

2. Medications


Some medications can slow your heart rate. This is often an expected response to the medication and is not always cause for concern. For example, some people take medication to slow their heart rate if they have abnormally fast heart rhythms (such as atrial fibrillation).

Other medications that may slow your heart rate include painkillers, sedatives, psychiatric medications, and medications for hepatitis C.

In some cases, these medications may be too strong and make your heart beat too slowly. If you’ve recently begun taking new medication and notice your heart rate is slower—and are experiencing any of the symptoms listed above—tell your doctor. They may want to monitor your heart rate or have you stop taking the medication.

3. Heart attack


Heart attacks occur because of a decrease in blood flow to the heart. This is caused by a blockage in one of the heart’s major blood vessels. In about 15% to 25% of heart attacks, the blood vessel that’s blocked also supplies oxygen to your heart’s electrical system. When the heart doesn’t get enough oxygen, you may experience a slow heart rate.

Call 911 or go to the ER right away if you suspect you’re having a heart attack. Treatment depends on the severity of the heart attack. It may include a combination of medications, stents (small mesh tubes that hold narrowed arteries open), and surgery.

Treating a heart attack usually restores normal heart rate. However, a small percentage of people may need to get a pacemaker to control their heart rate.

4. Obstructive sleep apnea


Obstructive sleep apnea is a sleep-related breathing disorder that causes people to struggle to get enough air flow into their lungs while asleep. This causes frequent pauses in breathing. Although people may not realize it, their sleep suffers as a result.

During these pauses in breathing, heart rate can become even slower than it usually does during sleep. This and the constant awakenings lead to excessive daytime sleepiness.

The most common cause of sleep apnea is an obstruction caused by excessive soft tissue in the mouth. The condition typically affects overweight and obese people, and it is more common in men.

If you have symptoms of sleep apnea, see your doctor. Untreated sleep apnea can lead to elevated blood pressure, slow heart rate, and abnormal heart rhythms.

Sleep apnea can usually be treated by wearing an airway pressure device while you sleep. This helps ensure you get enough air flow into your lungs.

Dr. Rx

It’s a common misconception that if you have a slow heart rate you have a “heart problem.”  It is important to remember that while this may be true, this is not an absolute. Athletes and younger adults can have naturally slower heart rates due to more efficient heart muscle. —Dr. Patel

5. Heart infection


  • Slow heart rate
  • Fatigue
  • Chest pain
  • Shortness of breath
  • Leg swelling
  • Fevers
  • Nausea
  • Possible recent illness

Myocarditis and endocarditis are inflammations of the heart. Myocarditis occurs when the inflammation affects the heart muscle (the myocardium). Endocarditis occurs when the inflammation affects the inner lining of the heart (the endocardium).

Myocarditis and endocarditis can slow your heart rate by damaging the electrical “wiring” that runs through the heart muscle or near the lining of the heart.

Both conditions are most commonly caused by infections that spread to the heart. They are a rare complication of any viral, bacterial, parasitic, or fungal infection you may have had. Myocarditis can also be caused by medications (such as cancer treatments), autoimmune disease, or a history of radiation exposure.

Treating the cause of myocarditis or endocarditis often restores your normal heart rate, though sometimes a pacemaker may be necessary to maintain it.

6. Hypothyroidism


Hypothyroidism, or “underactive thyroid,” means that the thyroid gland in the neck does not produce enough hormones. These hormones control many functions in the body, including your metabolism. When your thyroid is underactive, your metabolism slows, which causes a slower heart rate.

Hypothyroidism can be caused by an autoimmune disease, surgery or radiation treatment to the thyroid gland, certain medications, pregnancy, or consuming too much or too little iodine. It often develops in older women who have a family history of hypothyroidism.

If left untreated, these symptoms can worsen and lead to a very dangerous condition involving low blood pressure, significantly low body temperature, and possibly a coma.

Hypothyroidism is treated with oral hormone supplementation.

Other possible causes

A number of other conditions can cause a slowed heart rate:

  • Congenital heart defects
  • Vitamin deficiencies such as beriberi (low thiamine)
  • Infections such as Lyme disease or Chagas disease
  • Hypothermia (low body temperature that’s usually caused by exposure to cold temperatures)
  • Anorexia

When to call the doctor

Keep an eye on other symptoms you may have along with your slow heart rate. This is because a slow heart rate may not be worrisome if you’re otherwise feeling well. Call your doctor if you have any of the following:

  • Heart palpitations
  • Lightheadedness or dizziness when standing or resting
  • Decline in your energy level and ability to function

Pro Tip

Another important question to ask your doctor is: Will I need a pacemaker to treat my slow heart rate? —Dr. Patel

Should I go to the ER for a slow heart rate?

You should go to the ER if you have any of these signs of a more serious problem:

  • Chest pain or tightness
  • Swollen limbs
  • Dizziness
  • Confusion
  • Shortness of breath
  • Fever
  • Chills
  • Loss of consciousness


At-home care

  • Monitor your heart rate so you know what’s normal for you. While there is a medical definition for what is considered normal and what is considered slow, your heart may be pumping just fine at a slower heart rate.
  • Stay hydrated.
  • Exercise regularly (aerobic exercise and strength training).
  • Eat a diet rich in leafy greens.
  • Eat less meat.

Other treatment options

  • Medical treatment for a slow heart rate depends on what causes it. If there is a reversible cause, such as low thyroid hormone levels, the first step is to treat that cause.
  • A pacemaker may be necessary if your slow heart rate persists despite treatment of reversible causes or if the cause can’t be identified.
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UCLA Health Cardiology Fellow
Dr. Patel is a cardiology fellow at the University of California, Los Angeles. He received his undergraduate degrees in Mathematics and Psychology at the University of Illinois at Chicago, where he was a student in the Guaranteed Pre-Professional Admissions Program. After graduating summa cum laude with 2 degrees in 3 years, he matriculated to medical school at the University of Illinois. He compl...
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