What Causes a Fluctuating Heart Rate?

Most fluctuations in heart rate (aka pulse) are normal responses to the rhythms of daily life due to things like stress, sleep or a morning cup of coffee.

But it's important to understand what your heart rate is, why it might be fluctuating and when to get medical help.

After all, your heart rate "is one of the most sensitive markers to understanding what's happening with your heart," says Suzanne Steinbaum, DO, a cardiologist in New York City.

"Heart rate is the number of times the heart beats per minute," explains Sameer Arora, MD, a cardiologist with the University of North Carolina School of Medicine in Chapel Hill.

Your heart rate reflects how fast your heart is contracting or pumping blood through your body, adds Mark Lahiri, MD, a cardiac electrophysiologist at Henry Ford Health System in Detroit.

The normal range is 60 to 100 beats per minute (bpm), but this varies from person to person. One person's normal may hover at the upper end of the spectrum while another settles in the lower range. Athletes tend to have lower-than-usual heart rates.

Typically, a lower heart rate is better. "The slower it is, the more efficient your heart is working," says Dr. Steinbaum. "Your arteries and heart are dilating [opening] and flexible, so your heart doesn't have to work as hard."

Bear in mind that a heart rate that exceeds 100 bpm or drops below 60 bpm doesn't necessarily indicate that anything is wrong.

Your resting heart rate is when your heart is doing the least amount of work. That's measured when you're sleeping, sitting or lying down and feeling calm and relaxed. Things like your age, sex and physical fitness can affect your resting heart rate.

Plenty of everyday things cause heart rates to fluctuate. You can expect your pulse to change throughout the day as your heart adjusts to different energy needs.

Moving your body increases your heart rate.

"When you're exercising, your muscles demand a lot more oxygen, so your brain increases your heart rate so you have more," explains Michael Goyfman MD, chief of cardiology at Long Island Jewish Forest Hills in New York City.

Anger, stress, anxiety and pain (even stubbing your toe) can all cause your pulse to quicken.

"The body releases neurochemicals like adrenaline into the bloodstream that cause us to increase our heart rate and get that jittery feeling when we're angry or in pain," says Daniel Cantillon, MD, a cardiologist with the Cleveland Clinic.

Your pulse will move faster and slower with your respiratory cycle. "That's a very normal thing and a sign of good heart health," says Dr. Lahiri.

And anything else that alters your breathing pattern can affect your pulse. Your heart will slow down with meditation, for example.

Dehydration can alter your heart rate, as can caffeine and other stimulants.

Over-the-counter medications like decongestants, prescription drugs like beta blockers and vitamins can also change your pulse.

Medical issues — many of them easily treated — can also cause a fluctuating pulse, including:

1. ​Anemia or blood loss.​ "The blood cells aren't carrying enough oxygen, so a rise in heart rate compensates for diminished oxygen," says Dr. Cantillon.
2. ​Fever or infection​
3. ​An overactive thyroid gland​ (hyperthyroidism) will speed up your heart rate. "The thyroid regulates your metabolism, so if it's too high, your heart might beat faster than normal," says Dr. Lahiri.
4. ​An underactive thyroid​ (hypothyroidism) can have the opposite effect, often slowing your heart rate.
5. ​Having diabetes, underweight or overweight​ can all make the heart work faster.
6. ​Sleep apnea​
7. ​Hypertension​
8. ​A heart attack or previous heart problems​

Heart rate is not the same as heart rhythm, but the two are closely related. Rhythm refers to the electrical system of the heart. Irregular heart beat, known as arrhythmias, can cause your heart to beat outside of its normal rhythm, says Dr. Arora. And arrhythmias can sometimes cause wildly fluctuating heart rates.

There are several types of arrhythmias, including:

Atrial fibrillation is the most common type of arrhythmia in the U.S. "The electrical signals fire very erratically, and it causes the heart to beat [abnormally]," says Dr. Lahiri.

This often causes a rapid heart rate, too, according to the Mayo Clinic, ranging from 100 to 175 beats per minute, and episodes may come and go.

Heart defects or damage can lead to AFib, and having obesity, high blood pressure, a metabolic disorder, kidney or lung disease, diabetes or sleep apnea can all increase your risk. Sometimes AFib can be triggered by viral infections or stress.

Other symptoms of atrial fibrillation include:

• Heart palpitations, which feel like your heart is racing or flip-flopping
• Weakness
• Tiredness
• Decreased ability to exercise
• Feeling lightheaded or dizzy
• Shortness of breath
• Chest pain

Like AFib, an atrial flutter happens when electrical signals get mixed up, and the upper chambers of the heart pump very rapidly, per Johns Hopkins Medicine. It usually only occurs in older adults (over age 50), and having heart surgery puts you at higher risk.

SVT is marked by periods when you have a very fast heart beat, in the range of 150 to 220 beats per minute, per the Mayo Clinic. These episodes may last anywhere from a few minutes to a few days.

Triggers like stress, lack of sleep, caffeine, alcohol, smoking or exercise can bring on SVT, or it may be a symptom related to heart, lung or thyroid disease.

Most of the time, a fluctuating heart rate — whether it's too fast or too slow — will fix itself.

If it's caused by an underlying condition, though, treating the condition can help stabilize your pulse. For example, your doctor might prescribe iron supplements if you have anemia, or medication to correct a thyroid disorder.

Arrhythmias are more complex and require a complete work-up by a cardiologist, but those can usually be managed with lifestyle changes or medications.

You should seek medical help right away if you feel chest pain, high heart rate at rest (also called palpitations) or shortness of breath out of proportion to what would be expected for the degree of activity, says Dr. Arora. "Chest pain associated with sweating and nausea is particularly concerning, as that can be due to a heart attack," he adds.

Other red flags can include feeling weak, dizzy or lightheaded.

You can take your own heart rate easily by putting a finger over your pulse at the wrist, inside of your elbow, side of your neck or top of your foot. Simply count the number of beats in 60 seconds (or the number of beats in 15 seconds, then multiply that number by four).

To get the most accurate measure of your resting heart rate, follow these tips from Harvard Health Publishing:

• Wait at least two hours after exercise or a stressful event
• Wait at least an hour after having caffeine
• Don't measure when you've been sitting or standing for a long period of time

You can also monitor your heart rate throughout the day by wearing a fitness tracker, which may help you identify a fluctuating heart rate. But keep in mind that accuracy can vary in these products.

If you're concerned that you might have an arrhythmia, the best way to know for sure is by visiting a cardiologist, who can use more sophisticated heart monitors and tools like an electrocardiogram to track of your heart's activity.