A person’s heart rate may become dangerous if it is too high or too low. However, many factors can affect when a heart rate is dangerous.
The heart rate changes throughout the day to accommodate the demands of the body. It is higher during times of intense activity and lowest when a person relaxes or sleeps.
The heart rate also changes during pregnancy, fever, and times of anxiety.
Identifying a person’s usual heart rate pattern can help them understand what a dangerous heart rate is for them personally.
Ideal heart rates
A person should undergo regular checks to determine their heart rates at rest and while exercising. This could help them understand if there are any changes in their heart rate that could be dangerous.
According to the American Heart Association (AHA), a normal resting heart rate is 60–100 beats per minute (bpm) for most adults.
However, some people have heart rates outside of these ranges and are still perfectly healthy. For example, an elite athlete might have a very low resting heart rate of 40 bpm.
The heart rate greatly increases when a person is very active or exercising.
The highest rate a person’s heart can safely reach is their maximum heart rate. This declines with age. The ideal heart rate, or target heart rate, for exercise also declines with age.
In general, for most adults, the target and maximum heart rates are as follows:
|Age (years)||Target heart rate (bpm)||Average maximum heart rate (bpm)|
A person’s heart rate increase during exercise depends on many factors, including how intense the workout is and how fit they are.
A very sedentary person might find that their heart rate increases when walking from one room to another.
People who exercise regularly may need very intense workouts to get their heart rate up.
If a person’s heart rate is temporarily outside of these numbers during exercise, it is not usually a medical emergency. According to the AHA, a person can push themselves a little more or less depending on their heart rate target.
For most people, their sleeping heart rate will fall to the lower end of the normal resting heart rate range of 60–100 bpm.
In deep sleep, the heart rate may fall below 60 bpm, especially in people who have very low heart rates while awake.
After waking, a person’s heart rate will begin increasing toward their usual resting heart rate.
Children, especially young children, tend to have higher heart rates than adults.
Like adults, factors such as anxiety, fever, and heat may influence their heart rate.
This table shows the ideal heart rate ranges for children during wakefulness and sleep:
|Age||Heart rate when awake (bpm)||Heart rate when asleep (bpm)|
|under 28 days||100–205||90–160|
Many different factors can influence a person’s heart rate.
In most cases, having a very high or very low heart rate is only dangerous when there is not an obvious explanation.
High heart rate
Some factors that may cause a high heart rate include:
- Anxiety: People who are experiencing intense anxiety may have heart rates higher than 100 bpm, especially during a panic attack.
- Pain: Pain can cause the heart rate to climb much higher.
- Pregnancy: A person’s heart rate increases if they are pregnant. Normal activities also require more cardiovascular effort, so a person may find that relatively easy activities such as climbing stairs or taking short walks can cause the heart rate to climb much higher than usual. Pregnancy may also cause heart palpitations or an irregular heart rate.
- Fever: A fever can sometimes cause a higher heart rate. A person may also have a higher heart rate in intense heat.
- Caffeine: Caffeine increases both heart rate and blood pressure. If a person has recently had caffeine and notices a higher heart rate, this might be why.
- Medications: Some medications, such as serotonin or attention deficit hyperactivity disorder drugs, may also change the heart rate. Call a doctor if the heart rate suddenly changes after taking a new medication.
It is important to keep in mind that panicking about having a high heart rate may cause it to become even higher. Taking a few deep breaths and trying calming exercises may help a person assess whether or not their heart rate really is dangerous.
If there is an obvious cause of a heart rate change, such as pain or a fever, try addressing that first to see if the heart rate returns to normal.
Postural orthostatic tachycardia syndrome
A person with postural orthostatic tachycardia syndrome (POTS) may experience an increased heart rate upon standing up. They may also experience dizziness and a drop in blood pressure.
POTS is a condition of the autonomic nervous system. It happens because this system does not properly regulate bodily functions such as blood pressure, heart rate, or breathing.
Low heart rate
In general, the lower a person’s resting heart rate, the healthier their heart muscle. However, a very low heart rate in those who are not athletic or healthy can be a sign of a condition affecting the electrical system of the heart.
A sudden drop in heart rate far below a person’s usual resting heart rate may indicate sepsis (a potentially life threatening systemic infection), a brain bleed, or the electrical system of the heart failing.
In a person with any symptoms of illness, excessive bleeding, a recent serious injury, fainting, or dizziness, a low heart rate is an emergency.
According to one 2020 article, the following factors may lead to a person experiencing a low heart rate:
- chest trauma
- heart disease
- heart attack
- treatment for congenital heart disease
- sick sinus syndrome
- radiation therapy
- Lyme disease
- rheumatic fever
- collagen vascular disease
- muscular dystrophy
The following medications could also cause a low heart rate:
- calcium channel blockers
Determining the cause of a low heart rate means that a doctor can treat it accordingly. This may involve treating an underlying condition or changing the person’s medication.
Having a heart rate that is consistently outside of the ideal ranges above could lead to complications.
Low heart rate
Without appropriate treatment, a low heart rate can cause:
Over time, both high and low heart rates may damage the heart.
Having a very low heart rate can also damage the heart and other organs. This is more commonly associated with low blood pressure or other signs of shock.
High heart rate
Without proper treatment, a very high heart rate can lead to:
For most people, having a heart rate that is consistently too high or too low may signal an underlying condition, such as:
- damage to the heart’s valves or electrical system
- heart disease
- chronic or systemic infections
- issues with the thyroid
- anxiety disorder
- congestive heart failure
When to contact a doctor
It is not an emergency if the heart rate briefly falls outside of the recommended range or if a person has a shift in heart rate that improves with relaxation or deep breathing.
However, a person should contact a doctor if they:
- notice that their resting heart rate suddenly changes
- have a change in heart rate that causes anxiety
- experience a heart rate change after taking a new medication
- often have an irregular heart rate
A person should go to the emergency room if they:
- have shortness of breath and a change of heart rate
- feel very dizzy, faint, lightheaded, or confused
- have chest pain and a high or low heart rate
- have an infection and a low heart rate
- are bleeding and have a low heart rate, which might be the case if a person who has recently given birth experiences a change in heart rate