Why your resting heart rate changes

Are Heart Rate and Pulse Rate the Same?

Heart rate counts the heart’s beats over a given time. Pulse rate counts the pressure waves you can feel in an artery, such as at your wrist. Usually the two match. With some arrhythmias, however, a heartbeat does not produce a strong enough pulse to be felt at the wrist, so the pulse count can be lower.^[5]

A Faster Pulse When Breathing In Can Be Normal

Even at rest, the pulse may become slightly faster as you breathe in and slower as you breathe out. This normal variation is called respiratory sinus arrhythmia and is especially common in healthy children and young adults. Despite its name, it is usually not a disease. A new irregular pulse should not, however, be assumed to be this harmless variation based on a sensation or pulse number alone.^[9]

There Is More Than One “Usual” Pulse

A study of wearable data from 92,457 people found an overall average resting heart rate of about 65. Individuals’ average values ranged from approximately 40 to 109. The study had no clinical data to establish participants’ health, so that observed spread is not a healthy reference interval. A wearable’s calculated daily resting heart rate also differs from a single seated manual pulse measurement.^[4]

Within an individual, readings were much more stable. The median measure of within-week variation was about three beats, and around 80% of participants had a difference of less than 10 beats even in their most variable week. These research observations are not personal thresholds for deciding when medical attention is needed.^[4]

A reading of 70 may be ordinary for one person and higher than usual for another. Just as you have a usual body temperature, you can have a usual pulse. A baseline can help you notice a change, but cannot diagnose a condition or show that you are disease-free simply because the number is familiar.

Age and Sex Make Some Difference

In the same study, average resting heart rate rose until around age 50 and then declined, and women had higher averages than men across age groups. Lower averages were associated with 7–7.5 hours of sleep, while being underweight or having obesity was associated with higher averages. Yet age, sex, body size, and sleep together explained only about one tenth of the differences between people. These are observational associations, not proof that a particular sleep duration will lower anyone’s pulse.^[4]

Prepare for Repeatable Online Measurements

Resting readings are easier to compare when taken at a similar time, in the same position, and under similar conditions. HeartScan uses your phone’s accelerometer to detect tiny chest vibrations using seismocardiography (SCG), not a camera. Recline comfortably and follow the tool’s guidance for starting and placing your phone on your chest. A heart rate estimate is not the same as an ECG assessment of heart rhythm.

For two weeks, Misaki checks her readings while seated after her morning wash. They fall between 60 and 64, giving her a usual value of about 62. A reading in bed is not taken under exactly the same conditions, so she uses the seated routine for future comparisons.

1. Avoid measuring immediately after exercise. Rest for about five minutes, and recline comfortably for your HeartScan measurement.
2. Use a similar time and posture for comparisons, and consider recent activity, stress, fever, and medications when interpreting readings.^[1][5]
3. Open the HeartScan online tool and follow its guidance for starting, placing your phone on your chest, and remaining still.
4. If you want to compare readings over time, make your own note of the displayed pulse rate, date, time, posture, and how you feel. Seek medical advice for persistent unexplained changes or an irregular pulse.^[1][5]

Things That Can Temporarily Raise Heart Rate

Sleep and season can also be associated with resting heart rate. In the study of about 90,000 people, average rates were lowest among those sleeping 7–7.5 hours. Across the study population, rates were highest in early January and lowest in late July, a difference of about two beats. These group patterns do not mean every person follows the same seasonal rhythm.^[4]

Other medicines can slow the heart, including beta blockers and certain calcium channel blockers. Medication is important context when interpreting your usual pulse. Do not stop a prescribed medicine or change its dose on your own.^[1]

• Emotional or physical stress, including anxiety and pain.^[1][2]
• A brief increase just after standing up.^[1]
• Hot conditions or a rise in body temperature.^[1]
• Caffeine, alcohol, and smoking; individual responses vary.^[2]
• Some cold and allergy medicines containing stimulants such as pseudoephedrine.^[11]
• Fever and infection.^[10]

When the Increase Persists

An unexplained high resting heart rate can be associated with conditions such as anemia, respiratory disease, an overactive thyroid, or heart failure. A pulse number cannot distinguish these causes.^[10]

The reason for a change and how long it lasts matter as much as the number. A temporary rise that resolves when its trigger passes differs from an unexplained, sustained change. A rhythm that suddenly starts and stops, or becomes irregular, raises a different set of questions covered in Chapter 7.

• If there is an apparent trigger such as nervousness, the pulse returns to normal with rest, and there are no other symptoms, recording the pattern can be useful.^[10]
• Seek medical advice if readings remain higher than usual without a clear reason, or resting heart rate stays above 100. An ECG may be needed.^[5][10]
• For chest pain, severe breathlessness, fainting, marked dizziness, or palpitations with a cold sweat, call your local emergency number now. Do not assume anxiety or wait for the pulse to exceed 100.^[1][5]

Fever and Pulse Are Related, but Not by a Personal Formula

A small Finnish study compared ECG recordings from 27 young men during a febrile illness and after recovery. During fever, their average temperature was 38.4°C and their average heart rate was 84; after recovery, average heart rate was 66.5. Within that study, each 1°C increase was associated with an average increase of about 8.5 beats per minute, and heart rate also remained elevated during sleep.^[12]

That average from a small group of young men is not a reliable formula for predicting your own heart rate. Medicines, the illness itself, and your usual pulse can also affect the result. Misaki’s reading of 73 should not be declared safe because it appears to fit a calculation based on the study.^[1][12]

A Small Signal of Illness, Not a Diagnosis

In the United States, resting heart rate and sleep data from more than 47,000 wearable users improved estimates of state-level influenza-like illness activity. This was population surveillance, not a way to diagnose influenza in an individual.^[13]

In a study of 32 people with COVID-19, 26 showed an increase in resting heart rate; changes were detected as early as 10 days before symptoms in some participants. This was a small study. A smartwatch cannot establish infection, and an unchanged reading cannot rule it out. Knowing your usual pulse may help you notice that something has changed, rather than tell you exactly what is wrong.^[14]

Your Pulse May Take Time to Return After Illness

In data from 234 people with COVID-19, resting heart rate returned to its previous level an average of 79 days after symptom onset, later than step counts or sleep duration. About 14% still had a resting rate more than five beats above baseline beyond 133 days. These results describe that study group; they are neither an individual recovery timetable nor a period during which it is necessarily safe to wait.^[15]

Recovery can continue after a fever ends. Persistent or worsening symptoms and heart rate changes deserve medical advice rather than an assumption that they are simply part of recovery.

What If There Is No Fever?

Possible contributors include changes before symptoms appear or during recovery, stimulant ingredients in some cold medicines, and altered sleep while unwell. The pulse alone cannot identify which explanation applies.^{[4][11][14][15]}

Seek medical advice if resting heart rate stays above 100. If there is chest pain, severe breathlessness, fainting, or marked dizziness, call your local emergency number now rather than blaming a cold. Emergency symptoms matter regardless of the pulse count.^[1][5]

In Misaki’s story, her fever ends after three days, but her morning pulse stays around 66–68 for a little longer. Feeling not quite back to normal, she eases her schedule and goes to bed earlier. This fictional course is not a rule that the same readings make medical care unnecessary.

How Much Might It Change?

The analysis found larger reductions among people with higher starting heart rates and smaller effects at older ages. Misaki’s change from 62 to 58 is similar in size to the average percentage change in endurance groups, but a study average cannot promise an individual result. Nor does an unchanged resting pulse mean exercise has no value.^[16]

What Changes Inside the Heart?

Training can help the heart pump blood more efficiently, allowing it to meet resting needs with fewer beats. Changes in autonomic regulation can also contribute.^[1][8]

Animal research suggests the sinus node itself may change too. Trained mice retained a slower heart rate even when autonomic influences were blocked with drugs. They also had reduced HCN4, an ion channel involved in pacemaker activity. This experiment does not, by itself, fully explain training effects in humans.^[17]

Clinicians also consider how heart rate falls after exercise. Heart rate recovery depends on exercise intensity, whether recovery involves walking or complete rest, body position, medications, and the time of measurement. There is no single one-minute drop that everyone should use to declare their recovery normal. Seek advice if your heart rate does not rise much with exercise or if exercise brings unusual symptoms.^[10]

Lower Is Not Always Better

Highly trained athletes can have very low resting heart rates. Athlete ECG criteria can regard sinus rates of at least 30 as a normal finding under specific conditions, including no symptoms and an appropriate rise with activity. This is not permission for the general public to wait until their pulse reaches 30 before seeking advice.^[18]

Long-term, high-intensity endurance sport has separate considerations. A study of 52,755 Swedish long-distance cross-country skiers found an approximately 30% higher arrhythmia risk associated with completing at least five races over 10 years or racing faster. This observational finding does not show that jogging several times a week is dangerous.^[19]

• A slow pulse with fatigue, breathlessness, or dizziness needs medical advice. Fainting, severe breathlessness, or chest pain requires a call to your local emergency number now.^[1][5]
• Heart-rate-lowering medicines and strong vagal influences can also cause a low pulse; exercise is not the only explanation.^[1][2]
• Even athletes may need assessment for profound slowing or long pauses. Athlete criteria use rates of 30 or below or pauses of at least three seconds as prompts for evaluation, but symptoms must not be ignored while waiting for those numbers.^[18]

The Number Depends on the Source

One analysis of mammals reported an average lifetime total of about 730 million heartbeats. Other writing describes about 800 million. Species differ, and sources use different estimates. Two billion should not be treated as a precise universal law; it is better read as an illustration of a broad relationship across species.^[21][22]

Suppose we applied two billion to a person. At 70 beats per minute, the heart beats about 37 million times a year and would reach two billion in approximately 54 years. Average life expectancy in Japan is far longer. This arithmetic does not determine a human lifespan.

A Gauge, Not a Remaining Balance

Heart rate can be understood as a marker of physiological processes such as metabolism. That does not mean making the heart beat more slowly, by itself, extends life.^[21]

In humans, a meta-analysis of 46 studies involving about 1.25 million people found that each 10-beat higher resting heart rate was associated with a 9% higher relative risk of death from any cause and an 8% higher relative risk of cardiovascular death. A group with rates above 80 had a 45% higher relative risk of all-cause death than the lowest-rate comparison group. These are population-level relative associations, not a calculation of an individual’s probability of dying or remaining years.^[23]

Such risk associations also provide context for Japanese screening reference intervals. They do not create an immediate danger line at 85 beats per minute. Fitness, stress, sleep, and disease can all influence heart rate. Association is not the same as causation, and you should not change medication yourself to chase a lower number.^[3][23]

Your heartbeat is not a shrinking balance of beats left to spend. It is more useful to think of it as a gauge that offers clues about your current condition.

Premature Beats: Why a Beat Can Feel “Skipped”

An electrical impulse outside the sinus node can trigger a beat earlier than expected. That early contraction may not send a strong enough pulse to the wrist, making it feel as if a beat was missed.^[5]

Premature atrial beats occur in healthy people and may go unnoticed. Coffee, tea, alcohol, and some cold medicines can act as triggers for some people. Premature ventricular beats are also common and become more frequent with age. They are often benign without underlying heart disease, but frequent beats or an existing heart condition need assessment.^[11][24]

In the story, Misaki returns to two coffees a day and goes to bed earlier; eventually she no longer notices the thump. That fictional improvement does not establish the cause or identify her rhythm. Palpitations accompanied by chest pain can also occur with conditions such as angina or a heart attack: call your local emergency number now.^[5]

Atrial Fibrillation: An Irregularly Irregular Pulse

In atrial fibrillation, electrical activity in the atria becomes disorganized, often making the pulse intervals irregular. Blood clots can form in the atria and travel to a brain artery, causing an ischemic stroke.^[5]

Using data from about 630,000 Japanese health-checkup participants aged 40 or older in 2003, researchers estimated about 700,000 people with atrial fibrillation in Japan in 2005. Later public information describes an estimated total above one million. These are historical estimates and educational materials, not a measured 2026 count. Atrial fibrillation becomes more common with age.^[26][27]

Misaki’s 82-year-old grandmother has no symptoms. Her doctor notices an irregular pulse, and an ECG identifies atrial fibrillation. In Japan, March 9 is promoted as Pulse Day, and March 9–15 as Atrial Fibrillation Week, raising awareness of the condition.^[27]

• Public education materials describe an approximately fivefold higher risk of ischemic stroke with atrial fibrillation. An individual’s risk varies with age and other medical conditions.^[28]
• Strokes caused by clots from the heart can be severe. A 2014 information release reports about 20% mortality and about 40% needing care, including people left bedridden. These population figures do not predict an individual’s outcome.^[28]
• Intermittent atrial fibrillation may cause no symptoms, making ECG confirmation important. Appropriate anticoagulation helps prevent stroke; the same material cites a reduction of about 60%. A clinician must weigh treatment benefits against bleeding risk and other individual factors.^[28]

Paroxysmal Supraventricular Tachycardia: A Sudden Start and Stop

A very fast, regular rhythm can begin and end abruptly, like a switch being turned on and off. The source describes rates of 160–220 beats per minute, episodes lasting minutes to hours, and occurrence in younger people. Matching those numbers alone does not diagnose supraventricular tachycardia.^[25]

Palpitations may come with breathlessness, chest pain, or lightheadedness, and treatments are available. Many episodes are not immediately life-threatening, but you should not decide on your own that a fast rhythm is safe. A first sudden episode or recurring attacks need medical advice. With chest pain, severe breathlessness, fainting, or similar emergency symptoms, call your local emergency number now.^[25]

Bradyarrhythmias: A Rhythm That Is Too Slow

Problems generating or conducting the heart’s electrical signals can slow the pulse. Strong vagal effects can also cause slowing. These possibilities require a different assessment from an asymptomatic slow pulse in someone who trains regularly.^[2][5]

A slow pulse with unusual mental fogginess, breathlessness, or feeling faint needs medical evaluation. For fainting, altered consciousness, or severe breathlessness, call your local emergency number now. Do not wait to count a particular low rate or time a pause of several seconds.^[1][5]

What Online Measurement Can and Cannot Tell You

HeartScan online measurement estimates heart rate from tiny chest vibrations detected by your phone’s accelerometer, using seismocardiography (SCG). It is not an ECG, which records the heart’s electrical activity. The displayed number cannot diagnose atrial fibrillation or another rhythm disorder, and a usual reading cannot rule one out. A new or recurring irregular pulse needs clinical assessment with an ECG or other appropriate rhythm testing.^[5][28]

Note the displayed reading, symptoms, start time, duration, and measurement conditions to tell your clinician. An intermittent arrhythmia may have ended by the time you are examined. For chest pain, severe breathlessness, fainting, or other emergency symptoms, prioritize emergency help over another measurement or completing notes.^[1][5][28]

Arrange Medical Advice Promptly

The following are reasons to seek advice, not diagnoses. Training and medications can make a low pulse usual for some people. Explain whether the pattern is new and whether you have symptoms.^[1][5]

• A resting pulse that persistently exceeds 100 or remains below 50.^[5]
• A newly irregular rhythm or repeated episodes of irregularity.^[5]
• A sustained change from your usual rate with fatigue or mild dizziness.^[1]
• Resting readings that stay elevated over several days without a clear explanation.^[10]
• Little rise in heart rate with exercise, or unusual symptoms during activity.^[10]

Call Your Local Emergency Number Now

Call your local emergency number now for chest pain or pressure, severe breathlessness, fainting, altered consciousness, marked dizziness or feeling about to pass out, or palpitations accompanied by a cold sweat. Do not wait for a pulse above 100, below 50, or a pause lasting a certain number of seconds. A reading within a usual range cannot rule out an emergency.^[1][5]

• A suddenly fast or slow pulse accompanied by chest pain or severe breathlessness.^[1]
• Palpitations with a cold sweat, marked dizziness, or a feeling that you may faint.^[5]
• A slow pulse with fainting, altered consciousness, or severe difficulty breathing.^[5]

What to Tell Your Clinician

Routine notes can help an assessment, but never gather them at the expense of emergency care. Even if an episode has stopped, its start time and duration can be valuable because arrhythmias often come and go.^[5][28]

• Your usual pulse and the reading that concerned you.^[5]
• Whether the rhythm was regular or felt as if it skipped.^[5]
• Symptoms such as fatigue, dizziness, breathlessness, or chest pain.^[5]
• When the episode began, how long it lasted, what you were doing, and any medicines you take.^[1][28]