If you track your heart rate with a fitness monitor, you may notice it fluctuates throughout the day. A low heart rate is normal at certain times of the day, but you may wonder if it’s too low.
Keep reading to learn what a dangerously low heart rate is, its potential causes, and when to worry about a low heart rate.
Normal Resting Heart Rate
Adults’ resting heart rate ranges from 60 to 100 beats per minute. But everyone’s resting heart rate varies throughout the day depending on these and other factors:
- Age.
- Caffeine, alcohol, and nicotine use.
- Emotions, especially stress.
- Fitness level.
- Outside temperature.
- Whether they’re awake or sleeping.
Bradycardia is the medical term for low heart rate (fewer than 60 beats per minute). But bradycardia isn’t always a health problem. Many people, especially those who are physically fit, have a low heart rate while asleep or at rest.
It’s common for adults to have a heart rate of 40 to 50 beats per minute while asleep. It’s also normal for your heart rate to vary during sleep cycles. It’s usually lowest when you’re in a deep sleep cycle.
But when you’re awake, your heart rate naturally increases and usually falls into that average resting heart rate range. Your heart rate must speed up as needed, like when moving and exercising. The more active you are, the more oxygen-rich blood your body and brain need.
What’s a Dangerously Low Heart Rate?
A dangerously low heart rate is when your heart doesn’t pump faster when awake or moving. However, how low is too low depends on your age, fitness level, health, and whether you have bradycardia symptoms.
If your heart beats too slowly, it might not pump enough blood and oxygen to your brain and organs. That can affect how they work. Blood may also pool in your heart, increasing your risk of a stroke or heart failure.
Occasional or borderline bradycardia is usually not a problem as long as you don’t have symptoms and your heart rate increases to keep up with your activity. But too low a heart rate all of the time (or frequently) can cause symptoms such as:
- Chest pain.
- Confusion or memory problems.
- Difficulty exercising.
- Dizziness or lightheadedness.
- Fainting.
- Fatigue or low energy.
- Heart palpitations.
- Shortness of breath.
Causes of Low Heart Rate
Many things can cause a low heart rate; some are more serious than others. Some of the most common causes and risk factors include:
- Certain health conditions, like sleep apnea, hypothyroid (underactive thyroid), lupus, or high blood pressure.
- Congenital (present from birth) heart disease that affects the structure or function of your heart.
- Electrolyte imbalances.
- Heart damage from aging, coronary artery disease, or a heart attack.
- Medications like beta blockers that slow your heart rhythm or blood pressure.
- Problems with your heart’s natural pacemaker, such as a condition called heart block.
- Regular physical activity. This is a positive reason for a slower heart rate. Exercise strengthens your heart, so it doesn’t have to work as hard.
Bradycardia is more likely if you have several of these risk factors, especially if you’re older.
When Do You Know a Low Heart Rate Is Serious?
In extreme cases, low heart rate can cause serious and life-threatening symptoms, including:
- Cardiac arrest.
- Frequent dizziness and fainting.
- Heart failure.
- Seizures.
Therefore, you should call your doctor if you have frequent low heart rate symptoms, especially trouble breathing or extreme fatigue. Also, contact your doctor if your heart rate is consistently low — say below 50 beats per minute — and you’re not an athlete.
Evaluating Low Heart Rate
The first step in evaluating a heart rate problem is for your doctor to listen to your heart with a stethoscope. They’ll also review your medical history and medications. You can easily correct some heart rate problems by:
- Adjusting or changing your medication.
- Correcting an electrolyte imbalance.
- Treating underlying health conditions like sleep apnea or an underactive thyroid.
If these don’t work or aren’t applicable, your doctor may recommend these or other tests to discover the cause of your bradycardia:
- An electrocardiogram (EKG or ECG) — This test checks for problems with your heart’s electrical system. It uses electrodes (small sticky patches) applied to your chest. The electrodes connect to a machine that records your heart’s activity as you lie still.
- Electrophysiology (EP) study — This test uses a catheter (a thin, flexible tube) threaded through your blood vessels and into your heart to map electrical impulses.
- An exercise stress test — During this test, you walk on a treadmill or ride a stationary bike while hooked up to an EKG (electrocardiogram) machine. The machine records your heart’s activity to see how it adapts to increased activity.
- A Holter monitor — This portable EKG also records your heart activity using electrodes applied to your chest. You wear the electrodes and carry the small machine for several days while recording your activities and symptoms. Because you can’t predict when heart palpitations will happen, this test allows your doctor to monitor your heart for an extended period.
Treatments for Low Heart Rate
Borderline or occasional low heart rate without symptoms may not need treatment. But if necessary, your doctor might recommend:
- An implantable cardioverter defibrillator (ICD). An ICD is a small electronic device implanted under the skin to continuously monitor the heart’s electrical activity. If it detects an irregular or slow heartbeat, the ICD sends an electric impulse to the heart to restore normal rhythm.
- A pacemaker. This tiny, battery-powered, computer-like device regulates your heartbeat. A doctor uses a catheter to connect the pacemaker lead to your heart. They’ll permanently implant the pacemaker under your skin, usually in your upper chest.
A low heart rate is normal at certain times of the day. But you may need treatment if your heart doesn’t speed up when necessary. Contacting your health care provider when you have symptoms or questions is always wise.