A dangerous heart rate involves more than just your BPM — here are red flags that something’s wrong

• A normal heart rate is between 60 to 100 beats per minute (BPM), but it can vary by person.
• A heart rate slower than 60 BPM can be a sign of anything from a high fitness level to hypothyroidism. 
• A heart rate faster than 100 BPM can be due to smoking, exercise, or serious cardiac conditions. 

What is a dangerous heart rate?

Your heart rate refers to the number of times that your heart beats in a minute, which you can measure manually or check with a heart rate monitor. 

The normal heart rate is typically between 60 to 100 beats per minute (BPM). If you go outside this range, you experience either of the following:

• Bradycardia: A slow heart rate beating fewer than 60 times a minute.
• Tachycardia: A fast heart rate beating over 100 times a minute.

However, having a resting heart rate outside of the 60 to 100 BPM is not necessarily dangerous, says Dr. Jim Liu, a cardiologist at The Ohio State University Wexner Medical Center.

By itself, the heart rate is not always meaningful because it still depends on the individual, their symptoms, potential underlying causes, and the overall heart rhythm, he adds. 

Here's what you need to know about the heart rate and when you should seek medical attention.

Normal variations in heart rate

It's normal for heart rates to fluctuate widely based on what's going on with the body, Liu says. For instance, your heart rate typically increases during exercise or in times of stress, while it can decrease and fall below 60 BPM during sleep.

Other variables could affect your heart rate, such as:

• Temperature
• Body position
• Emotions, like stress, excitement, or anxiety
• Body size
• Medications
• Age

Here is a chart showing how the normal resting heart rate changes with age:

In general, a heart rate that's normal for you might not necessarily be normal for somebody else. Therefore, it's difficult to establish a universal heart rate that is considered dangerous for everyone.

"Some individuals may be able to tolerate a certain heart rate better than others, whereas other individuals who may have underlying heart problems or other medical conditions may not tolerate those same heart rates," Liu says.

What could cause a heart rate that is too slow?

A low heart rate — less than 60 BPM — is not always concerning because it can be due to a number of factors.

For example, the following could result in a low heart rate:

• Good fitness level: "Athletes typically have a much lower resting heart rate when compared to everyone else," says Dr. Emad Aziz, section chief of cardiac electrophysiology at the Rutgers New Jersey Medical School.
• Medications: Certain medications like beta-blockers, which are used to treat high blood pressure, may cause a low heart rate.
• Age: A lower resting heart rate is more common in older individuals, Liu says. 

It's important to consider the heart rate with the heart rhythm and any concerning symptoms. If you have a heart rate around 40 BPM, but your heart has a normal rhythm and you don't have any concerning symptoms, it's not necessarily dangerous, Liu says. 

On the other hand, if your heart rate is about 50 BPM but you have symptoms like dizziness, weakness, or confusion, you would need immediate medical attention. 

Serious causes of a slow heart rate may include:

• Myocarditis or inflammation of heart tissue
• Damage to heart tissues from heart disease or heart attack
• A complication from a heart surgery
• Hypothyroidism, or when the thyroid isn't producing enough hormone
• A symptom of a virus like Covid-19

What could cause a heart rate that is too fast?

A fast heart rate is a normal physiologic response to a lot of different things, Liu says. Any of the following may drive the heart rate up:

• Smoking
• Heavy alcohol use
• High levels of caffeine
• Medications
• Exercise
• Stress

It may be concerning if the fast heart rate is due to problems with the electrical signals in the heart, says Aziz. These electrical abnormalities lead to irregular heart rhythms that can cause:

• Atrial fibrillation
• Atrial flutter
• Ventricular fibrillation

"A normal heart rhythm with rates around 120s may not be considered dangerous, but someone with a serious arrhythmia like atrial fibrillation in those same heart rates would be considered differently," Liu says.

When to see a doctor immediately

According to Aziz and Liu, you should seek medical attention if an abnormal heart rate — whether too slow or too fast — occurs with the following symptoms:

• Chest pain
• Progressive shortness of breath
• Dyspnea on exertion, or shortness of breath during physical activity
• Syncope or passing out
• Severe pounding in the chest
• Dizziness
• Lightheadedness

If you are concerned with any new or sudden irregularities with your heartbeat, consult an electrophysiologist, a cardiologist that specializes in heart rhythm abnormalities, Aziz says.

Insider's takeaway

Your normal heart rate depends on various factors like your age and physical fitness. By itself, a slow or fast heart rate is not necessarily concerning.

"The heart rates have to be taken into context with respect to symptoms, rhythm, and what else is going on with the patient," Liu says.

If you feel chest pain, shortness of breath, or dizziness, seek medical attention immediately.