What Is a Dangerous Heart Rate?

In general, a dangerous heart rate for an adult is above 100 beats per minute (bpm) at rest or less than 60 beats per minute (bpm) at rest. However, many factors determine whether a heart rate is dangerous, such as a person’s age and activity level and any underlying health problems they have or medications they take.

This article will go over normal heart rates for adults and children, and how too-high or too-low heart rates can be harmful to your health.

Adult Heart Rate

When you’re active during the day, your heart pumps faster to get oxygen to your muscles. This makes your heart rate go up. At night, when your body is at rest, your heart rate tends to go down.

Dangerous Heart Rate for Adults

The thresholds for a dangerous heart rate at rest or a maximum heart rate when active depend on your overall health, age, fitness level, and any medical conditions you have or medications you take. 

That said, you can have a resting heart rate that’s outside this range and still be healthy. For example, if you are regularly very physically active, a resting heart rate of 40 beats per minute might be normal for you.

Similarly, someone who is very fit might be able safely to achieve a faster heart rate while they’re exercising and a lower resting heart rate than someone who does not regularly exercise.

Normal Heart Rate at Rest for Adults

For most adults, a resting heart rate should be between 60 bpm and 100 bpm. 

Having a high heart rate when you’re not being active can be a sign of a problem. For example, having a heart rate over 120 while resting could point to an abnormal heart rhythm.

Normal Heart Rate While Exercising for Adults

It can be normal to have a higher heart rate when you’re exercising. A high heart rate during exercise is considered safe as long as you do not go above your maximum heart rate.

Maximum heart rate varies from person to person, but in general, you can figure out your maximum heart rate by subtracting your age from 220. 

For example, a young athlete may reach a heart rate of 170 bpm while exercising. However, if you had this heart rate when at rest, it would not be normal. 

Normal Heart Rate While Sleeping for Adults

Your heart rate goes down when you’re sleeping, even below 60 bpm. However, if it goes too low, that can be dangerous. 

Having a high heart rate while you’re sleeping could be a sign of an underlying health problem or sleep disorder like sleep apnea.

Child Heart Rates

Normal heart rates and safe levels for active and resting heart rates differ among children and adults. In fact, what's okay varies by a child's age.

Dangerous Heart Rates in Children

What is considered a dangerous heart rate for a child depends on what heart rate is considered normal for their age.

In general, a dangerous heart rate for an infant or child falls out of the normal range for their age group, which is shown in the table below. 

Causes of Heart Rate Problems in Children

If a child’s heart rate is too high or too low, it can be caused by many of the same problems that cause heart rate issues in adults—for example, an underlying health condition or a medication side effect. 

Sometimes, heart rate problems are the first signs that a child was born with a heart defect. 

It can be hard to know when a child is having abnormal heart rates, especially if they are not talking yet. Older children can often say that they feel faint or weak or describe having a funny feeling in their chest (heart palpitations). 

Additional symptoms of abnormal heart rates in younger kids can include:

• Pale skin
• Tiredness
• Irritability
• Difficulty feeding
• Shortness of breath

High Heart Rates

Having a heart rate that's too high is called tachycardia. In general, tachycardia means having a heart rate that is above 100 bpm. Tachycardia can be dangerous but is not always.

Types

There are different types of tachycardia. Having a higher heart rate can be normal while you’re exercising, for example. You can also get tachycardia:

• During scary or stressful events
• When you consume a lot of caffeine
• If you are a heavy smoker
• If you have an overactive thyroid (hyperthyroidism)

Tachycardia can also happen when the electrical signals in your heart that cause it to beat are firing abnormally. Since your heart is beating faster than it should, it can't fill back up with blood completely. As a result, less blood gets delivered to the rest of your body.

In some cases, tachycardia does not cause any symptoms. When it does, a high heart rate can cause symptoms like:

• Dizziness
• Fainting
• Pounding heartbeat
• Chest pain or pressure
• Shortness of breath
• Palpitations (fast-beating, fluttering, or pounding heartbeats)
• Tiredness

Frequently going above a safe maximum heart rate can be dangerous because an overworked heart is less efficient at pumping blood throughout the body. This can result in loss of consciousness or a heart attack.

Causes

Common causes of a high heart rate include anxiety, dehydration, illnesses and fever, substance use (including caffeine), and medications. 

Some health conditions like abnormal levels of certain blood cells and nutrients (like red blood cells or calcium), blood pressure problems, heart disorders, and thyroid conditions can also make your heart rate higher than normal.

You may also have a high resting heart rate if you have obesity or are not physically fit. 

There are also potentially serious causes of a high heart rate, including a blood infection called sepsis and a heart rhythm problem called ventricular tachycardia.

Low Heart Rate

A heart rate that is considered too low is called bradycardia. This typically means a heart rate lower than 60 bpm for adults.

Types

A low heart rate is not always abnormal—it can even be a sign of physical fitness.

For example, if you are an endurance athlete, your heart probably works very efficiently. Your normal heart rate could be closer to 40 or 50 beats per minute—or even lower. This means that your heart does not have to pump as fast to deliver oxygen to the rest of your body as someone else’s would. 

However, bradycardia can also be a symptom of underlying medical conditions. 

For example, a low heart rate can occur when electrical impulses do not travel along the right paths in the heart or when structures that generate electrical impulses are damaged.

Low heart rate can also be from heart disease, heart attack, and other medical conditions such as hypothyroidism (underactive thyroid).

The symptoms of bradycardia are similar to those caused by a high heart rate and can include:

• Dizziness
• Fainting
• Difficulty breathing
• Confusion
• Weakness
• Tiredness
• Limited ability to exercise

Causes

A low resting heart rate is sometimes normal—for example, well-trained athletes can have a resting heart rate under 60 bpm, and that’s normal for them. 

However, just like with a higher-than-normal heart rate, a low heart rate can also be a sign of a medical problem or a medication side effect.

Common causes of a low heart rate include having high levels of certain nutrients in the blood (calcium, potassium), having a body temperature that is too low, thyroid problems, autoimmune diseases (e.g., lupus), heart problems, and certain medications (e.g., beta-blockers). 

There are also serious causes of a low heart rate like high pressure in the brain, inflammation of the heart muscle, or heart block.

Heart Rate and Arrhythmias

Heart rate problems can also be caused by issues with how the heart beats. When the heartbeats are abnormal, it’s called an arrhythmia. 

Arrhythmias can make the heart beat too fast or too slow, or beat irregularly (“skipping” a beat).

While arrhythmias are often treatable, it’s important to find out if you have one and what kind you have. Some of them can be life-threatening.  

Heart rates outside the normal range in children can be caused by some of the same issues that affect adults—the abnormal firing of electrical signals in the heart or damage to the heart. It can also be a side effect of medication.

Arrhythmias in Children

It can be more difficult to know when a child is experiencing abnormal heart rates, especially if they are too young to talk. Older children might know that they feel faint or weak or are experiencing heart palpitations. Additional symptoms in younger kids can include:

• Pale skin
• Tiredness
• Irritability
• Difficulty feeding
• Shortness of breath
  

Risks of an Abnormal Heart Rate

Having a heartbeat that is too fast or too slow, especially over a long time, can lead to serious health problems. 

High Heart Rate Risks

A high heart rate can give you unpleasant symptoms like passing out (fainting or syncope), chest pain, shortness of breath, palpitations, and dizziness.

Having a high heart rate that goes on without treatment can make the heart weak. The strain on the heart can eventually lead to heart failure. 

If a high heart rate is being caused by a problem like a dangerous arrhythmia, it can be fatal—and possibly without warning.

Low Heart Rate Risks

Having a low heart rate can lead to complications of heart failure and changes in blood pressure (both high and low).

When to See a Healthcare Provider

If your heart rate is consistently out of the normal range for adults, or if you are having symptoms such as dizziness or shortness of breath, you should see a healthcare provider.

If you think that you or your child has a heart rate that is too high or too low, testing can be done to figure out what’s causing it.

For example, an electrocardiogram (ECG or EKG) is usually the first test done to determine the cause of an abnormal heart rate. 

During this test, electrodes are attached to your chest (and sometimes arms or legs) to pick up on the electrical impulses as they pass through your heart.

Your provider might also have you wear a portable heart monitor for a day or longer to record your heartbeat. 

Tell your provider about any medications, over-the-counter (OTC) products, or supplements that you are taking, as certain drugs affect your heart rate. 

For example, beta-blockers slow your heart down, while decongestants can increase your heart rate.

When to Call 911

Sometimes, a change in your heart rate can be a sign of a serious health problem. 

Seek immediate medical attention or call 911 if you get any of these symptoms suddenly and severely:

• Chest pain or pressure
• Jaw, arm, neck, or back pain
• Difficulty breathing
• Weakness
• Dizziness/fainting
• Fatigue
• Nausea/vomiting

How to Check Your Own Heart Rate

To measure your heart rate, place your index and middle fingers at the side of your neck or the inside of your wrist and count the number of beats (pulses) for one minute.

Just make sure you are not taking your heart rate when you’re stressed, ill, have recently used substances like nicotine and caffeine, just finished a meal, or were just working out. These activities can all affect your heart rate, so wait an hour or two before trying to get a measurement.

How to Raise Your Heart Rate

If you have a low resting heart rate, it might be normal and not something you should be worried about. If your heart rate is low because you’re very physically fit, it can be a positive thing and you may not need to try to raise it.

If your heart rate is too low and it’s not healthy for you, your provider might recommend some steps you can take on your own to try to get your heart rate up. You may also need medical treatment to address the underlying cause of your low heart rate.

You might be able to raise your heart rate by:

• Exercising as recommended by your provider
• Making sure you’re hydrated
• Avoid having large, heavy meals and instead have frequent, smaller, nutritious meals and snacks throughout the day

How to Lower Your Heart Rate

There are a few strategies you can use to calm a racing heart. However, know that if there is an underlying health problem causing your heart rate to be too fast, you might need medical treatment. 

You might be able to lower your heart rate by:

• Finding ways to relieve stress
• Treating and managing anxiety
• Quitting substances like tobacco and limiting alcohol and caffeine
• Getting to and staying at a weight that supports your health
• Making sleep a priority 
• Doing physical activity as recommended by your provider

Summary

A normal resting heart rate for adults is 60 to 100 beats per minute. However, a normal heart rate varies from person to person, and your ideal heart rate might be higher or lower than this range.

Many factors can cause a heart rate to be too high or too low, including exercising, consuming caffeine, and smoking. In some cases, a heart rate that is too high or too low is a sign of underlying problems with the electrical impulses in your heart, other medical conditions, or even a side effect of a medication you’re taking. 

If you have an abnormal heartbeat and other symptoms like chest pain and shortness of breath, don’t wait to get medical attention. 

It might be that the cause of your heart beating faster or slower is nothing to worry about, but since there’s a chance of it being a serious health problem, it’s better to know for sure.