What Is a Dangerous Resting Heart Rate? When Should You Go to the ER?

A resting heart rate can change throughout the day. Stress, anxiety, exercise, illness, medications, caffeine, dehydration, and even body position can temporarily affect how fast the heart beats. For most adults, a resting heart rate between 60 and 100 beats per minute is generally considered normal. However, the number alone does not always tell the full story.

A resting heart rate that is unusually high, unusually low, or suddenly different from your normal pattern can sometimes signal a heart rhythm problem or another medical condition. More importantly, a heart rate becomes much more concerning when it occurs with chest pain, shortness of breath, fainting, severe dizziness, confusion, weakness, or other signs of poor blood flow.

What Is a Normal Resting Heart Rate?

For most adults, a resting heart rate of 60 to 100 beats per minute is considered within the normal range. Resting heart rate means how many times the heart beats each minute when the body is at rest, rather than immediately after exercise or physical activity.

However, normal does not mean identical for everyone. A healthy, physically fit person may have a resting heart rate below 60 beats per minute without having a heart problem. Athletes and highly conditioned people can sometimes have resting rates around 40 to 60 beats per minute. Heart rate may also naturally decrease during sleep.

On the other hand, a person who normally has a resting heart rate around 65 beats per minute may notice a significant change if the rate repeatedly rises to 110 or 120 while sitting quietly. That change may deserve medical attention even though the number itself is not automatically an emergency.

This is why doctors consider the heart rate together with symptoms, medical history, medications, recent illness, hydration status, physical condition, and the heart rhythm itself.

What Is a Dangerous Resting Heart Rate When It Is High?

A resting heart rate above 100 beats per minute is generally called tachycardia. A high resting heart rate does not automatically mean that the heart is failing or that a person is having a heart attack. Sometimes the heart is beating faster because the body is responding to another problem.

For example, fever, dehydration, stress, anxiety, pain, certain medications, and other conditions can cause the heart to beat faster. In these situations, the fast heart rate may be a response to something else rather than the primary problem.

Still, a persistent resting heart rate above 100 deserves attention, particularly if there is no obvious reason for the increase.

A heart rate of 105 while sitting quietly is different from a heart rate of 150 that suddenly starts while you are resting. The faster and more abrupt the change, the more important it is to consider the possibility of an abnormal rhythm.

Very rapid heart rates can also interfere with the heart’s ability to fill and pump blood efficiently. Some types of tachycardia, including certain ventricular rhythms, can be life-threatening.

Is a resting heart rate of 100 dangerous?

Not necessarily. A resting heart rate of exactly 100 beats per minute is at the upper end of the typical adult range. It can also temporarily rise because of stress, caffeine, illness, dehydration, or recent activity.

If the rate repeatedly stays around 100 or higher while completely at rest, particularly if this is new for you, it is reasonable to discuss it with a healthcare professional.

Is a resting heart rate of 120 dangerous?

A resting heart rate of 120 is clearly above the usual adult resting range. It does not automatically mean that you are experiencing a life-threatening emergency, but the reason for the elevated rate matters.

If your heart rate is 120 while resting and you also have chest discomfort, shortness of breath, dizziness, weakness, fainting, confusion, or a feeling that something is seriously wrong, emergency evaluation is appropriate.

Is a resting heart rate of 150 dangerous?

A resting heart rate around 150 is significantly elevated and should not simply be ignored, especially if it begins suddenly. Some abnormal rhythms can produce very fast heart rates with symptoms such as chest pain, dizziness, shortness of breath, weakness, or fainting.

Mayo Clinic recommends emergency medical care when a very fast heartbeat occurs with chest pain, shortness of breath, weakness, dizziness, or fainting.

What Is a Dangerous Resting Heart Rate When It Is Low?

A resting heart rate below 60 beats per minute is called bradycardia. But a low number is not automatically dangerous.

For example, a healthy athlete may have a resting heart rate below 60 because the heart can pump an adequate amount of blood with fewer beats. A lower heart rate can also occur during sleep.

The concern increases when the heart rate is unusually low for that particular person or when the slow rate causes symptoms.

Severe bradycardia can prevent enough oxygen-rich blood from reaching the brain and other organs. Symptoms can include dizziness, weakness, fatigue, shortness of breath, confusion, chest pain, fainting, or near-fainting.

Is a resting heart rate of 50 dangerous?

Not necessarily. A resting heart rate of 50 may be normal for a healthy, physically fit adult, particularly if there are no symptoms.

However, if a heart rate of 50 is unusual for you and you are experiencing dizziness, weakness, fainting, shortness of breath, or chest pain, it should be medically evaluated.

Is a resting heart rate of 40 dangerous?

A resting heart rate around 40 is low. It can occur normally in some highly trained athletes, but it may be concerning in other adults, especially if it is new or accompanied by symptoms.

A very slow heart rate combined with fainting, difficulty breathing, chest pain, confusion, or severe weakness should be treated as an emergency.

The key question is not simply, “How low is too low?” It is also, “Is the heart rate low enough to affect blood flow to the brain and other organs?”

When Does Heart Rate Become a Medical Emergency?

There is no single heart-rate number that determines whether every person needs emergency care. Symptoms and the underlying cause matter.

For example, a healthy athlete with a resting heart rate of 48 and no symptoms may not need emergency treatment. Meanwhile, another person with a heart rate of 110 could require immediate evaluation if the rate is new and accompanied by chest pressure and difficulty breathing.

The combination of an abnormal heart rate and symptoms is often much more important than the number alone.

Emergency warning signs include:

• Chest pain, pressure, tightness, or discomfort
• Shortness of breath or difficulty breathing
• Fainting or feeling as though you are about to faint
• Severe dizziness or lightheadedness
• New confusion
• Severe weakness
• A very rapid heartbeat that does not settle
• A new irregular or pounding heartbeat accompanied by concerning symptoms
• Blue or gray lips or skin
• Collapse or loss of consciousness

The National Heart, Lung, and Blood Institute notes that arrhythmias can cause chest discomfort, difficulty breathing, dizziness, fainting, weakness, and other symptoms. Serious symptoms such as difficulty breathing or chest pain warrant emergency medical care.

Symptoms That Make an Abnormal Heart Rate More Concerning

Heart rhythm problems can look very different from one person to another. Some people notice only a racing or pounding sensation. Others experience dizziness, weakness, shortness of breath, chest pressure, or fainting.

Some arrhythmias may cause no noticeable symptoms at all. Others can interfere with the heart’s ability to deliver enough blood to the body.

Chest pain or pressure

Chest discomfort is one of the most important warning signs. A fast or irregular heartbeat with chest pressure can occur with an arrhythmia, but chest discomfort can also signal a heart attack or another emergency.

New, sudden, severe, or unexplained chest pain should not be assumed to be caused by anxiety or a fast heartbeat. Emergency evaluation may be necessary.

Shortness of breath

Difficulty breathing can occur when the heart is beating abnormally fast or slowly and is not pumping effectively. It can also occur with heart attack, lung disease, blood clots, pneumonia, asthma, and other serious conditions.

If a sudden abnormal heart rate is accompanied by significant trouble breathing, emergency medical care is appropriate.

Dizziness or fainting

Dizziness, near-fainting, and fainting can indicate that the brain is not receiving enough blood flow. These symptoms are particularly concerning when they occur during an episode of a very fast, very slow, or irregular heartbeat.

Do not drive yourself if you feel faint or unstable. Sit or lie down somewhere safe and seek emergency assistance when symptoms are severe.

Severe weakness or confusion

Extreme weakness, confusion, or a sudden change in alertness can indicate that the body is not receiving enough oxygenated blood or that another serious condition is occurring. These symptoms require prompt medical evaluation.

What Can Cause a High Resting Heart Rate?

A high resting heart rate can have many causes. The heart may be responding appropriately to a problem elsewhere in the body, or an abnormal electrical rhythm may be responsible.

Common causes include:

• Stress or anxiety
• Fever or infection
• Dehydration
• Pain
• Caffeine or other stimulants
• Some medications
• Anemia
• Overactive thyroid
• Low blood pressure
• Blood loss
• Heart rhythm disorders
• Heart or lung conditions

This is why treating the heart rate alone may not solve the problem. If dehydration, infection, anemia, thyroid disease, or another condition is causing the elevated pulse, the underlying problem also needs to be identified.

Can anxiety cause a high resting heart rate?

Yes. Anxiety activates the body’s stress response and can increase heart rate. A person may also notice pounding or racing heartbeats during a panic attack.

However, anxiety should not automatically be blamed for a new or unusually high resting heart rate. Anxiety and medical emergencies can produce overlapping symptoms. If the symptoms are new, severe, or accompanied by chest pain, difficulty breathing, fainting, or significant weakness, medical evaluation is safer than assuming anxiety is the cause.

Can dehydration raise your resting heart rate?

Yes. When the body loses fluid, the cardiovascular system may compensate by increasing the heart rate. Dehydration can occur with vomiting, diarrhea, fever, heavy sweating, poor fluid intake, or other illnesses.

A fast heart rate caused by dehydration may improve when the underlying problem is addressed, but significant dehydration can itself become an emergency, particularly when accompanied by confusion, fainting, severe weakness, or inability to keep fluids down.

What Can Cause a Low Resting Heart Rate?

A low resting heart rate can also have many causes. In some people it is simply a normal finding. In others, it may indicate a problem with the heart’s electrical system or another medical condition.

Possible causes include:

• High physical fitness or athletic training
• Sleep
• Certain medications
• Changes in the heart’s electrical conduction system
• Heart disease
• Previous heart damage
• Underactive thyroid
• Changes in potassium or calcium levels
• Inflammation affecting heart tissue
• Sleep apnea

Mayo Clinic notes that medications, heart disease, thyroid problems, electrolyte changes, inflammation, and other conditions can contribute to bradycardia.

A low pulse becomes more concerning when it is accompanied by symptoms showing that the body may not be receiving enough blood flow.

Could an Abnormal Resting Heart Rate Be an Arrhythmia?

Yes. An arrhythmia is a problem with the rate or rhythm of the heartbeat. The heart may beat too quickly, too slowly, or irregularly. Some arrhythmias are relatively harmless, while others can lead to serious complications.

People may describe an abnormal rhythm as:

• A racing heartbeat
• A pounding heartbeat
• Fluttering in the chest
• A skipped beat
• Pauses between beats
• An irregular heartbeat
• A heartbeat that suddenly becomes very fast
• A heartbeat that alternates between fast and slow

Atrial fibrillation is one example of an arrhythmia. It may cause fatigue, palpitations, shortness of breath, chest pain, dizziness, or fainting, although some people have no obvious symptoms. Untreated atrial fibrillation can increase the risk of serious complications, including stroke and heart failure.

Other rhythms, such as supraventricular tachycardia, can cause sudden episodes of a very fast heartbeat. Emergency care is recommended when a very fast heartbeat lasts for more than a few minutes or occurs with chest pain, dizziness, shortness of breath, or weakness.

How Should You Check Your Resting Heart Rate?

If a smartwatch, fitness tracker, blood pressure monitor, or manual pulse check shows an unusual heart rate, take a moment to assess the situation before repeatedly checking the number.

Sit quietly and allow your body to rest. Avoid checking immediately after climbing stairs, exercising, walking quickly, drinking caffeine, or experiencing a stressful event. Then check the pulse again.

You can measure your pulse at the wrist or neck, or use a reliable device. If the reading remains unusually high or low, make a note of the number and any symptoms you are experiencing.

It is also useful to know your normal resting heart rate. A sudden change from your usual pattern can provide important information for a healthcare professional.

Do not spend several minutes repeatedly checking a smartwatch while experiencing serious symptoms. Chest pain, severe shortness of breath, fainting, or severe dizziness should take priority over obtaining a more precise heart-rate reading.

How Does an ER Evaluate an Abnormal Heart Rate?

An emergency department does more than simply check the pulse. The goal is to determine why the heart rate is abnormal and whether the rhythm or underlying condition is putting the patient at immediate risk.

Vital signs and physical examination

The medical team may check heart rate, blood pressure, oxygen level, temperature, breathing rate, and other vital signs. The physical examination can provide clues about dehydration, infection, heart problems, breathing problems, or other conditions.

Electrocardiogram

An electrocardiogram, or EKG, records the heart’s electrical activity. It can help identify abnormal rhythms and provide important information about the heart’s rate and electrical pattern.

The American Heart Association notes that tachycardias are usually evaluated with an EKG.

Blood tests

Depending on the symptoms and suspected cause, blood tests may help identify problems such as electrolyte abnormalities, infection, anemia, or other conditions affecting the heart rate.

Additional testing

Some patients may need additional testing based on their symptoms. For example, someone with chest discomfort may require cardiac evaluation, while someone with significant breathing difficulty may need testing aimed at identifying a lung or cardiovascular problem.

The important point is that an abnormal pulse is a symptom or finding, not a diagnosis by itself. The emergency team needs to determine what is causing it.

When Should You Go to the ER?

Go to the ER or call 911 when an abnormal resting heart rate occurs with symptoms that could indicate a serious heart or circulation problem.

Seek emergency care for an unusually fast or slow heart rate accompanied by:

• Chest pain or pressure
• Shortness of breath
• Fainting or near-fainting
• Severe dizziness
• Confusion
• Severe weakness
• New or significant irregular heartbeat
• Persistent rapid heartbeat while resting
• Collapse or loss of consciousness

If you have already been diagnosed with an arrhythmia, follow the emergency plan provided by your healthcare professional. If symptoms are significantly different from your usual episodes, do not assume they are harmless simply because you have experienced palpitations before.

The situation may not require an emergency room visit, if the heart rate is abnormal but you feel completely well. However, a new, persistent, or repeatedly abnormal resting heart rate should still be discussed with a healthcare professional.

For questions about whether chest symptoms should be evaluated at an urgent care center or emergency room, Montrose Emergency Room also provides guidance on urgent care vs. ER for chest pain.

Similarly, symptoms involving difficulty breathing should not be dismissed when they occur with an abnormal heart rate. The urgent care vs. ER guide for shortness of breath explains why significant breathing difficulty may require emergency evaluation.

What Should You Do While Waiting for Emergency Help?

If you are experiencing a potentially dangerous heart-rate episode with severe symptoms, call 911 or your local emergency number. Do not drive yourself if you are faint, severely dizzy, confused, or having significant chest pain or breathing difficulty.

Sit or lie down somewhere safe while waiting for help. If possible, have another person stay with you.

Do not attempt to diagnose the rhythm from a smartwatch alone. A wearable device can provide useful information, but it does not replace an EKG or medical evaluation.

If someone becomes unconscious and is not breathing normally, emergency services should be contacted immediately and CPR should be started according to emergency instructions. An AED can be used if one is available.

Can a Dangerous Resting Heart Rate Be Prevented?

Not every abnormal heart rhythm can be prevented. Some are related to the heart’s electrical system, genetics, previous heart disease, or other factors outside a person’s control.

However, several habits can support cardiovascular health and reduce some factors that can contribute to abnormal heart rates.

Stay adequately hydrated, manage conditions such as high blood pressure and thyroid disease, take medications exactly as prescribed, avoid excessive stimulant use, get appropriate physical activity, and seek medical attention for persistent or unexplained changes in your heart rate.

It is also useful to learn what your usual resting heart rate looks like. Tracking trends can make it easier to recognize when something has changed.

However, heart-rate tracking should be used as a tool, not as a substitute for medical judgment. A normal-looking number does not guarantee that chest pain, fainting, or severe breathing difficulty is harmless.

Emergency Heart Care in Montrose Houston

When an abnormal heart rate occurs with concerning symptoms, timely evaluation matters. Montrose Emergency Room provides 24/7 emergency care in Houston and evaluates conditions involving chest pain and other potentially serious symptoms. The facility is located at 1110 W. Gray St #101, Houston, TX 77019, and the listed phone number is (832) 487-0911.

Montrose Emergency Room offers emergency evaluation with diagnostic capabilities that include EKGs, imaging, and laboratory services. These tools can help emergency physicians investigate symptoms rather than relying on the heart-rate number alone.

For patients experiencing significant chest pain, difficulty breathing, fainting, or other potentially life-threatening symptoms, calling 911 is the safest first step. Emergency medical services can begin care and determine the appropriate destination.

For less immediately dangerous but persistent concerns about an unusual resting heart rate, medical evaluation can help determine whether further cardiac testing or follow-up is appropriate.

Frequently Asked Questions

What is a dangerous resting heart rate?

There is no single number that is dangerous for every person. For most adults, 60 to 100 beats per minute is the usual resting range. A resting rate above 100 is called tachycardia, while a rate below 60 is called bradycardia. The level of concern depends on the number, whether it is new, how long it lasts, the person’s health, and whether symptoms are present.

Is a resting heart rate over 100 dangerous?

Not necessarily. A resting heart rate above 100 can occur because of stress, anxiety, fever, dehydration, pain, medications, or other conditions. However, persistent or unexplained tachycardia should be evaluated, especially if it occurs with chest pain, shortness of breath, dizziness, weakness, or fainting.

Is a resting heart rate of 120 an emergency?

A resting heart rate of 120 is significantly above the usual adult resting range, but the number alone does not determine whether it is an emergency. If the rate is persistent, suddenly started, or occurs with chest pain, difficulty breathing, fainting, severe dizziness, or weakness, seek emergency care.

Is a resting heart rate of 150 dangerous?

A resting heart rate around 150 is significantly elevated and can occur with some abnormal heart rhythms. If it starts suddenly or lasts more than a few minutes, particularly with chest pain, dizziness, shortness of breath, or weakness, call 911 or seek emergency medical care.

Is a resting heart rate below 60 dangerous?

Not always. Some healthy athletes naturally have resting heart rates below 60, and heart rate normally slows during sleep. A low resting heart rate becomes more concerning when it is new, unusually low for the person, or causes dizziness, fainting, shortness of breath, chest pain, confusion, or significant weakness.

Is a resting heart rate of 40 an emergency?

Not automatically. A heart rate around 40 can occur in some highly trained athletes. However, in a person who is not accustomed to having such a low heart rate, particularly when symptoms are present, medical evaluation is important. Fainting, difficulty breathing, or chest pain should be treated as emergency symptoms.

Can anxiety cause a high resting heart rate?

Yes. Anxiety and stress can activate the body’s fight-or-flight response and raise the heart rate. However, a new or unusually high resting heart rate should not automatically be attributed to anxiety, particularly when chest pain, breathing difficulty, fainting, severe dizziness, or weakness is present.

Can dehydration cause a fast resting heart rate?

Yes. Dehydration can cause the heart to beat faster as the body attempts to maintain circulation. Significant dehydration may also cause weakness, dizziness, reduced urination, confusion, or fainting and may require urgent or emergency treatment.

When should I call 911 for a fast heart rate?

Call 911 when a fast heart rate is accompanied by chest pain or pressure, significant shortness of breath, fainting, severe dizziness, confusion, severe weakness, or other signs of a potentially serious medical problem. Do not drive yourself if you are unstable or feel that you may pass out.

Can a smartwatch detect a dangerous heart rate?

A smartwatch can alert you to an unusually high, low, or irregular heart rate, but it cannot determine the cause by itself. If the reading is abnormal and you have concerning symptoms, medical evaluation is more important than repeatedly checking the device.

Final Thoughts

A dangerous resting heart rate is not defined by one universal number. For most adults, 60 to 100 beats per minute is the typical resting range, but healthy people can naturally fall outside that range. The more important question is whether the heart rate is unusual for you and whether it is affecting how you feel.

A persistently fast resting heart rate can result from something as temporary as stress, fever, dehydration, or pain, but it can also be associated with an abnormal heart rhythm or another medical condition. Likewise, a slow heart rate may be completely normal in a well-conditioned athlete but concerning when it causes fainting, dizziness, shortness of breath, chest pain, or weakness.

Do not ignore the combination of an abnormal heart rate and serious symptoms. Chest pain, difficulty breathing, fainting, severe dizziness, confusion, and significant weakness are reasons to seek emergency medical attention rather than waiting for the heart rate to normalize on its own.

If you are unsure whether symptoms require emergency care, it is safer to have potentially serious heart symptoms evaluated promptly. Early assessment can help identify dangerous rhythm problems and other conditions before they become more serious.

Medical Disclaimer: This article is intended for general educational purposes and does not diagnose or treat any medical condition. Heart-rate ranges can vary based on age, fitness, medications, health conditions, and individual circumstances. If you have chest pain, severe breathing difficulty, fainting, severe dizziness, confusion, or other potentially life-threatening symptoms, call 911 or your local emergency number immediately.