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What is a dangerous heart rate?

If the heart beats too fast or too slow, it can cause trouble. Learn the basics and when to see a health care provider.

Published: June 21, 2024 |3 minutes to read

Written by: Anastasia Climan

A patient sits on an exam table while their health care provider takes their blood pressure.

Note: If you have questions about your heart health, it’s best to talk with a trained health professional. If your health might be in immediate danger, call 911 or go to the nearest emergency room right away.

A beating heart is what keeps our bodies running like clockwork. However, if the rhythm is off, it could be a symptom of a larger issue.

The first thing you should do if you suspect something is wrong is contact your health care provider. Here are some things to know about irregular and dangerous heart rates.

In this article:

What are the types of dangerous heart rates?

Heart rates fluctuate naturally throughout the day. For example, your heart rate will be higher when exercising and lower when resting or sleeping. Heart rates can be a little different from person to person depending on factors like age and fitness level.

That said, when the heart beats too fast, too slow or too irregularly (out of sync), it could be a sign of a medical emergency. These are the three heart rates to pay special attention to.

A health care provider’s office is the first step if you’re concerned about your heart. They’ll look at your resting heart rate — the pace of your heart when you’re sitting. Most adults’ resting heart rate should be between 60 to 100 regularly spaced beats per minute (bpm). Any resting heart rate not within this range might be dangerous.1

What is tachycardia?

A resting heart rate of 100 bpm or faster is considered tachycardia (a rapid heart rate).2 Heart rates speed up in response to caffeine, exercise and stress. However, consistent tachycardia at rest can signal underlying health problems.

There are several forms of tachycardia. Some people are born with a structural abnormality of the heart that causes tachycardia. Other times, certain lifestyle factors or health conditions increase your risk for tachycardia.3 Symptoms of tachycardia can range from dizziness and chest pain to unconsciousness.

Identifying the problem early can help prevent serious complications. So, always speak to your health care provider to voice any concerns.4

What is bradycardia?

Bradycardia is the opposite of tachycardia. With bradycardia, the resting heart rate is too slow. For most adults, a heart rate under 60 bpm is considered bradycardia. However, it’s normal for well-trained athletes to have lower resting heart rates, even as low as 40 bpm.5 Bradycardia is also more common with advanced age.6

Certain health conditions, such as autoimmune disease, heart disease and hypothyroidism, may cause bradycardia. In addition, bradycardia is a known side effect of certain heart medications. Adults with bradycardia may feel weak and tired, especially after exercise. Serious complications of bradycardia can include fainting or heart failure.7

What is arrhythmia?

An arrhythmia is the catch-all term for any abnormal heart rate or rhythm. Tachycardia and bradycardia fall under this umbrella. Arrhythmias happen when the electrical signals responsible for regulating heart rate do not conduct correctly. As a result, the heart doesn’t beat as it should and the organs around the body don’t receive the right amount of blood and oxygen to function properly. If left untreated, it may cause damage to organs or result in full organ failure.8

When to go to an emergency room

A brief arrhythmia may go unnoticed, but a sustained arrhythmia can cause significant problems. In extreme cases, an abnormal heart rhythm can cause a sudden loss of heart function. This is called a cardiac arrest, which can be fatal without immediate action.9

Some reasons to call for an ambulance include:

  • Loss of consciousness
  • Prolonged palpitations (extra, irregular or skipped heartbeats)10
  • Racing heart rate
  • Severe chest pain
  • Shortness of breath

But the list may be much larger. If you’re concerned about your own heart rate or rhythm, speak to a health care provider as soon as you can.

This content is for informational purposes only and is not medical advice. Consult your health care provider before taking any vitamins or supplements and prior to beginning or changing any health care practices.