When is a Heart Rate Considered Dangerous?

Generally, a dangerous heart rate for an adult is above 100 beats per minute (bpm) at rest or less than 60 bpm at rest. However, some individuals may experience slight variations in these heart rates. For example, fit individuals may have resting heart rates below 60 bpm.

Many factors determine whether a heart rate is dangerous, such as a person’s activity level, age, gender, and any underlying health problems or medications they take. A dangerous heart rate for a child can also vary significantly depending on their age.

Dangerous Heart Rate for Adults

A heart rate may signal an underlying health concern when the resting heart rate is above 100 bpm or under 60 bpm. A heart rate that is above 100 bpm and too fast is called tachycardia. A heart rate that is too slow and below 60 bpm is called bradycardia.

When you’re active during the day or exercising, 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. So, there are times during the day when it might be ok for your heart rate to go below 60 bpm or beyond 100 bpm. And if you're an athlete, your resting heart rate may be below 60 bpm.

There can be some variation between male and female hearts, and females tend to have a higher resting heart rate. However, if you are assigned female at birth, a resting heart rate above 100 bpm still warrants a call to your healthcare provider to check out potential underlying causes.

Adult Heart Rates and Exercise

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. Higher heart rates are expected when active and exercising, but they should return to between 60 and 100 bpm at rest. If it doesn't, check in with your healthcare provider.

Generally, your maximum heart rate is about 220 minus your age. So, if you are 40 years old, your maximum heart rate while exercising would be 220-40=180 bpm. While a heart rate of 180 may be safe during periods of vigorous exercise, it should not remain that high.

While moderately exercising, your target heart rate should be 50-70% of your maximum heart rate. So, if you're 40 years old, your maximum heart rate should be about 180 bpm, and your target heart rate should be between 90 and 126 bpm during moderate exercise. If you exercise vigorously, your heart rate may approach 85% of your maximum heart rate.

However, once you are done exercising, your heart rate should fall back below 100 bpm at rest. If you exercise regularly, a resting heart rate of 40 beats per minute might be normal for you.

Types of High Heart Rates

A heart rate that's too high is called tachycardia. In general, tachycardia means having a sustained heart rate above 100 bpm.

There are different types of tachycardia, including:

• Sinus tachycardia: This type happens when the electrical impulses that stimulate the heartbeat are abnormally fast. These electrical impulses are controlled by the sinus node, a small mass of tissue in the heart's upper right chamber that serves as the heart's pacemaker.
• Supraventricular tachycardia: This type originates from the upper chambers of the heart. Atrial fibrillation, the most common type of irregular heart rhythm, is a type of supraventricular tachycardia.
• Ventricular tachycardia: This type originates from the lower chambers of the heart.
• Junctional tachycardia: This type originates from the junction between the upper and lower chambers of the heart.
  

A higher heart rate can be normal in some situations, such as while exercising. 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)
• When sick, if you have a fever

Too fast heart rates reduce the heart's ability to pump blood throughout the body effectively and can lead to other health problems.

Symptoms of a High Heart Rate

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

Some of these symptoms are also symptoms of serious medical conditions such as a heart attack. Seek medical care if you are experiencing chest pain, difficulty breathing, or are concerned.

Causes of a High Heart Rate

There are several causes of a high heart rate. These include, but are not limited to:

• Anxiety
• Dehydration
• Illnesses and fevers
• Infections
• Substance use (including caffeine)
• Certain medications (e.g., stimulant medications such as Adderall)
• Medical conditions affecting blood cells, nutrients, and other blood contents (e.g., anemia)
• High blood pressure
• Heart conditions
• Arrhythmias (irregular heart rhythm)
• Hyperthyroidism
• Decreased fitness levels
• Overweight
• Sleep apnea

Your heart rate generally decreases while you sleep. If you notice that it increases during sleep, it can signal sleep apnea or another underlying cause.

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

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 try 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 
• Engaging in physical activity as recommended by your provider to lower your resting heart rate

Types of Low Heart Rates

A heart rate that is considered too low is called bradycardia. For adults, this typically means a heart rate lower than 60 bpm. However, athletes and fit individuals can have low resting heart rates.

There are different types of bradycardia:

• Sinus bradycardia: This describes a heart rate of less than 60 beats per minute. It is considered normal in physically fit people. Endurance athletes, for example, may have a normal heart rate closer to 40 or 50 bpm. Athletes' heart muscles typically do not have to pump as fast to deliver oxygen to the rest of their body as someone else’s would. 
• Sick sinus syndrome: This occurs when the sinus node isn't working correctly, and the electrical impulses that make your heart beat are too slow. People with this condition may also have pauses in their heartbeat.
• Tachycardia-bradycardia syndrome: This occurs in people who have a problem with the sinus node and atrial fibrillation, a common type of irregular heartbeat. It can cause alternating fast and slow heartbeats.
• Ectopic bradycardia: This happens when another part of the heart other than the sinus node functions as the heart's pacemaker.
• Heart block: This happens when something interferes with the electrical impulses that make the heart beat.

Symptoms of a Slow Heart Rate

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 of a Slow Heart Rate

Causes of bradycardia can include, but are not limited to:

• High fitness levels
• Medication side effects
• Chemical imbalances in the blood
• Low body temperature
• Hypothyroidism
• Heart conditions
• Autoimmune conditions

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. Alternatively, you can take your pulse for 15 seconds and multiply it by four. Many devices such as wearable fitness trackers and smart watches can also measure your heart rate and help you track it over time.

Keep in mind that if you take your heart rate when you’re stressed, ill, have recently used substances like nicotine and caffeine, or were recently working out, your heart rate might be higher than its usual baseline.

When to See a Healthcare Provider

If your heart rate is consistently out of the normal range or you are concerned about your heart function or that of your child, contact your healthcare provider.

Your healthcare provider can perform various tests to determine if your heart rate is too high or too low and the underlying cause.

Diagnostic Tests for Abnormal Heart Rates

Healthcare providers can use various tests to determine the underlying cause of abnormal heart rates. These tests include, but are not limited to:

• Electrocardiogram (ECG or EKG): This 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.
• Holter monitor: Your provider might also have you wear a portable EKG for a day or longer to record your heartbeat. 
• Stress test: During this test, your heart rate is monitored while you are on a treadmill. It is used to diagnose exercise-related heart rate problems.
• Tilt-table test: This test helps diagnose changes in heart rate when you switch between lying down and standing up.
• Imaging tests: Tests like a CT scan or an MRI can help find structural problems in your heart.
• Electrophysiologic testing: This procedure involves threading catheters through your veins to help record your heart's electrical signals. It is done under local anesthesia.

Tell your provider about any medications, over-the-counter (OTC) products, or supplements you are taking, as certain drugs affect your heart rate. For example, beta-blockers slow your heart down, while decongestants can increase it.

What Is a Dangerous Heart Rate for a Child?

Normal active and resting heart rates differ among children and adults, and the normal range for heart rates in children varies depending on age. Many causes of fast and slow heart rates are the same for children and adults, such as illness, fevers, infections, medications, cardiac conditions, and other health concerns.

If you are concerned that your child's heart rate is too fast or too slow, ask their healthcare provider for advice.

Summary

A normal resting heart rate for adults is 60 to 100 bpm. However, heart rates can vary 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, seek medical attention.