Sleep Heart Rate Chart: Normal Values, OSA Signs, and What to Watch

Last updated June 2026. Medically reviewed for accuracy. Reading time: approximately 12 minutes.

Category: Health — This article explains what your heart rate should look like across each sleep stage, what an abnormal pattern reveals, and how to interpret your wearable's overnight heart rate data. The interactive chart above lets you compare normal sleep with the OSA signature directly.

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The Direct Answer

A sleep heart rate chart shows how heart rate should change across a healthy night — and what deviation from that pattern signals:

Sleep Stage	Normal Heart Rate	Key Feature
Falling asleep / N1	55–65 bpm	Gradual decline from waking resting rate
Light sleep / N2	50–60 bpm	Continued decline; sleep spindles begin
Deep sleep / N3 (slow-wave)	40–50 bpm	Lowest point of the night; parasympathetic dominance
REM sleep	55–65 bpm (variable)	Brief rise; higher variability; dream-influenced
Brief awakenings	60–75 bpm	Spikes with arousal; should return to baseline quickly
OSA apnea episode	35–45 bpm (brady) → 80–95 bpm (tachy)	Sawtooth cyclic pattern — the CVHR signature

The chart above visualises these patterns across a full 8-hour night. Toggle between Normal, OSA, and Compare views to see how the two patterns differ. The key diagnostic insight: a hallmark electrophysiological feature of OSAS is the cyclical variation of heart rate (CVHR), a distinctive pattern observable on single-lead ECG recordings — bradycardia during apnea, followed by tachycardia on arousal, then normalisation — a sawtooth the chart makes immediately visible.

Why Heart Rate Changes During Sleep

Heart rate during sleep is not simply "low and stable." It follows a precise, stage-dependent pattern governed by the balance between the sympathetic (arousal) and parasympathetic (rest) arms of the autonomic nervous system.

Sleep onset and progression to deeper sleep stages is associated with a shift toward greater parasympathetic modulation, whereas rapid eye movement (REM) sleep is associated with a shift toward greater sympathetic modulation.

Understanding this shift — and why each stage produces a different heart rate — is the foundation for interpreting overnight heart rate data from any source.

N1 and N2: The Transition Into Sleep

As you move from wakefulness into light sleep, the parasympathetic nervous system begins to dominate. Heart rate declines steadily from your waking resting rate — typically 60–80 bpm for most adults — toward the 50–60 bpm range of established light sleep. When we enter light sleep, the heart rate gradually slows to around our resting heart rate.

This decline reflects the body shifting from active monitoring mode to restorative mode — reduced metabolic demand, lower sympathetic tone, and the beginning of the hormonal changes (cortisol decline, melatonin rise, growth hormone preparation) that define early sleep.

N3: The Lowest Heart Rate of the Night

Slow-wave sleep (N3) is where heart rate reaches its nightly minimum. During deep sleep, the heart rate decreases to its lowest levels — when you enter the deeper sleep stages, your heart rate can drop 20% to 30% below your resting heart rate.

For a person with a resting rate of 65 bpm, this means a deep sleep heart rate of approximately 45–52 bpm. For athletes and highly conditioned individuals, deep sleep heart rates of 35–40 bpm are not uncommon and are not pathological.

The mechanism: complete parasympathetic dominance, with vagal tone at its peak. NREM sleep is considered cardio-protective and increased high-frequency power during NREM sleep is a good indicator of cardiac health.

REM Sleep: Controlled Sympathetic Surges

REM sleep produces a characteristically different heart rate pattern — not a stable low, but a series of controlled elevations corresponding to dream content and sympathetic nervous system activation.

During REM sleep (the stage associated with vivid dreaming) your heart rate can fluctuate and may even briefly increase, reflecting the dream's activity level. The typical REM heart rate is 55–65 bpm — higher and more variable than N3, but lower and more controlled than wakefulness.

REM sleep is associated with surges in sympathetic nerve activity, heart rate, and blood pressure, as well as reduced baroreceptor sensitivity, challenging the cardiovascular system. This is clinically significant: the cardiovascular vulnerability during REM explains why cardiac events are disproportionately concentrated in the early morning hours — when REM cycles are longest and most intense.

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The Sleep Heart Rate Chart by Age

For most adults, a normal resting heart rate ranges from 60 to 100 beats per minute. During sleep, it is typical for the heart rate to decrease by about 20% to 30% compared to daytime rates. Applying this across age groups:

Age Group	Typical Resting HR	Normal Deep Sleep HR	Normal REM HR
Children (5–12)	70–100 bpm	55–75 bpm	65–85 bpm
Teenagers (13–18)	60–90 bpm	45–65 bpm	55–75 bpm
Young adults (19–35)	60–80 bpm	42–58 bpm	52–68 bpm
Middle-aged (36–60)	60–80 bpm	44–60 bpm	54–70 bpm
Older adults (60+)	60–80 bpm	46–62 bpm	56–72 bpm

Note: Trained athletes may have resting HRs of 40–50 bpm and deep sleep HRs of 33–42 bpm — not pathological when accompanied by normal waking function.

Red Flags: When the Numbers Warrant Attention

• Sleeping heart rate consistently above 90 bpm: a sleeping heart rate consistently above 90 beats per minute might indicate a problem, especially if it occurs alongside symptoms like night sweats, chest discomfort, or shortness of breath.
• Sleeping heart rate below 40 bpm (non-athlete): a significantly low sleeping heart rate, known as bradycardia, occurs when the heart beats fewer than 40 beats per minute during sleep. For non-athletes, an unusually slow heart rate could indicate issues such as an electrolyte imbalance, an underactive thyroid, or even heart disease.
• Highly irregular patterns: irregular patterns in sleeping heart rate are a reason to be concerned — according to research published in the Journal of the American College of Cardiology, people with irregular heart rhythms during sleep are at a higher risk of stroke and heart failure.
• The sawtooth CVHR pattern: repeated cycles of bradycardia-then-tachycardia throughout the night — visible in the OSA view of the chart above

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The OSA Heart Rate Signature: Cyclical Variation of Heart Rate (CVHR)

The most clinically important abnormal pattern visible on a sleep heart rate chart is the CVHR — the electrophysiological fingerprint of obstructive sleep apnea.

The Four-Phase CVHR Mechanism

During an obstructive apnea, the initial phase is characterised by bradycardia driven by the activation of pulmonary stretch receptors and enhanced vagal tone — the so-called 'diving reflex' response to hypoxemia and hypercapnia. As the apneic episode progresses, accumulating hypoxemia and hypercapnia progressively stimulate peripheral chemoreceptors (carotid bodies), generating a sympatho-excitatory surge that accelerates heart rate. At the moment of arousal and resumption of ventilation, a secondary tachycardia ensues due to sympathetic activation, followed by a vagally-mediated deceleration as breathing resumes.

This produces the four autonomic phases visible in the OSA view of the chart:

1. Phase A — Bradycardia (diving reflex): Heart rate drops to 35–45 bpm as the body's oxygen-conservation reflex activates
2. Phase B — Progressive tachycardia: As CO₂ accumulates and O₂ falls, chemoreceptors drive heart rate upward
3. Phase C — Post-arousal sympathetic spike: Heart rate peaks at 80–95 bpm as breathing resumes and the arousal system fires
4. Phase D — Normalisation: Vagal deceleration returns heart rate toward baseline before the next apneic event

This cyclical pattern — bradycardia during apnea, tachycardia on arousal, then normalisation — produces a characteristic oscillation in R-R intervals detectable on standard Holter or 30-second ECG strips.

CVHR as a Diagnostic Tool

The clinical value of CVHR extends beyond description. Studies analysing R-R interval variability of ECG during polysomnography have reported that the frequency of cyclic variation of heart rate reflects the AHI. Specifically: in a previous study of 864 polysomnographic subjects with suspected sleep apnea, the frequency of CVHR per hour during sleep was correlated with the AHI obtained from the simultaneous polysomnography with r = 0.84.

An r = 0.84 correlation means CVHR frequency is a strong predictor of apnea-hypopnea index — the primary OSA severity measure. This is why cardiologists can sometimes diagnose suspected OSA from a Holter ECG recording without polysomnography.

At onset of sleep apnoea all patients showed progressive bradycardia, followed by abrupt tachycardia on resumption of breathing. The electrocardiographic pattern, which is identifiable by computer analysis, can be used as a screening tool for sleep apnoea — it was not seen in controls without sleep apnoea syndrome.

What CVHR Means for Your Health

The CVHR pattern is not merely a diagnostic curiosity. Each apnea cycle represents a cardiovascular stress event:

1. Nocturnal hypertension — the post-arousal sympathetic spike elevates blood pressure repeatedly throughout the night, contributing to sustained hypertension even in patients whose daytime BP appears controlled
2. Arrhythmia risk — the sympathovagal imbalance has been noted to be the key trigger in cardiac arrhythmogenesis in OSA patients. Increased sympathetic tone and decreased parasympathetic tone have been reported in patients with OSA.
3. LV diastolic dysfunction — repeated CVHR cycles are associated with left ventricular diastolic dysfunction, independent of other cardiovascular risk factors
4. Atrial fibrillation — OSA-related autonomic dysregulation is a significant contributor to atrial fibrillation risk, particularly nocturnal AF

Use the Sleep Apnea Risk Screener if your wearable shows an elevated and irregular overnight heart rate pattern — particularly if you also snore, feel unrefreshed, or have been told you stop breathing during sleep.

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How to Read Your Wearable's Sleep Heart Rate Data

Most consumer wearables now display overnight heart rate graphs. The accuracy of these charts varies — and understanding what they can and cannot reliably show is essential for interpretation.

What Wearables Measure Well

• Overall nightly average heart rate: Good accuracy; correlates well with clinical measurements
• General trend pattern (decline → nadir → REM elevations): Moderate-to-good; most devices capture the broad shape correctly
• Minimum heart rate (deep sleep): Good accuracy; useful as a cardiovascular fitness and recovery indicator
• Heart rate variability (HRV): Variable by device; Oura Ring and Garmin have strongest validation datasets

What Wearables Struggle With

• Precise sleep stage assignment: Kappa values of 0.55–0.65 against PSG (see the tracking accuracy article); N3 is frequently underestimated
• CVHR detection: Most consumer apps do not explicitly flag CVHR; the sawtooth pattern may be visible on the raw heart rate chart but is not algorithmically identified by most devices
• Brief arousals: Wearables systematically miss short awakenings, which means some heart rate spikes during OSA may be attributed to "wake" when they are actually intra-sleep apnea events

Reading the Pattern — A Practical Guide

When reviewing your wearable's overnight heart rate graph, look for:

Healthy pattern:

• Smooth, progressive decline in the first 90 minutes of sleep
• A stable nadir period (the baseline of the deep sleep trough)
• 2–4 brief, smooth elevations corresponding to REM cycles, increasing in duration toward morning
• Return to near-resting-rate within 15–20 minutes of actual waking

Concerning patterns:

• Elevated baseline throughout the night (consistently above 70 bpm during what the device calls sleep)
• Multiple sharp, large-amplitude spikes (>20 bpm increase over minutes) that are not correlated with obvious awakenings
• No clear nadir — heart rate stays in the 60–70 bpm range throughout without a deep sleep trough
• Highly irregular pattern with no discernible stage structure

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Sleep Heart Rate and Sleep Debt

The Sleep Debt Calculator measures how many hours you are owed — but your sleep heart rate chart provides independent physiological evidence of sleep quality that complements the quantitative deficit measure.

The relationship between sleep debt and nocturnal heart rate is specific:

1. Elevated baseline nocturnal HR: Sleep debt raises overnight sympathetic tone, pushing the nightly heart rate baseline upward — a person accumulating sleep debt will often show a higher average nocturnal HR than their well-rested baseline
2. Blunted nadir: Deep sleep heart rate in the sleep-debt state is typically higher than baseline — the autonomic shift toward parasympathetic dominance that produces the N3 nadir is impaired by elevated cortisol from HPA axis dysregulation
3. Reduced HRV: Heart rate variability — the beat-to-beat variation that indicates parasympathetic flexibility — is a sensitive marker of recovery quality; sustained sleep debt reduces overnight HRV, visible in wearable data

A pattern of elevated nocturnal HR combined with the debt quantification from the Sleep Debt Calculator provides a more complete picture of sleep quality than either metric alone. Use the Sleep Quality Score to integrate both sources into a structured weekly assessment.

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The Sleep Heart Rate Self-Assessment

Use this checklist alongside the chart above to interpret your nightly data:

• My average overnight heart rate is consistently above 70 bpm
• My heart rate chart shows repeated sharp spikes that are not correlated with waking up
• I have no clear deep sleep nadir visible — heart rate stays relatively flat all night
• My minimum overnight heart rate has increased over recent weeks despite stable fitness
• My partner reports snoring or witnessed breathing pauses
• I feel unrefreshed in the morning despite 7–8 hours in bed
• My overnight HR is higher during periods of poor sleep or stress
• My wearable's HRV score has been declining week over week

Scoring:

• 0–2 checked: Heart rate pattern appears within normal range — continue monitoring
• 3–4 checked: Possible sleep debt or mild autonomic dysregulation — calculate your deficit at sleepdebtcalc.com and review sleep hygiene
• 5–8 checked: Elevated probability of OSA or significant sleep debt — use the Sleep Apnea Risk Screener and discuss with a healthcare provider

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Frequently Asked Questions

What is a normal heart rate during sleep?

For most healthy adults, a normal sleeping heart rate ranges from 40 to 60 bpm, though it can vary based on age, fitness level, and overall health. This slowdown occurs as part of your body's natural sleep cycle — particularly during deep non-REM sleep — when the parasympathetic nervous system becomes more active, promoting relaxation and energy conservation. REM sleep produces brief, controlled elevations to 55–65 bpm with higher variability. The reference chart above shows the expected pattern across a full night by sleep stage.

Why does heart rate go up during REM sleep?

REM sleep is associated with sympathetic nervous system activation — the same system that produces fight-or-flight arousal during waking. During REM, the brain is highly active (generating dreams), skeletal muscles are temporarily paralysed, but heart rate and breathing become irregular and can increase. Researchers believe that the surge in activity during REM sleep could explain why already vulnerable people often experience heart attacks and other events in the early morning hours, which is typically spent more in REM sleep.

What does a sleep apnea heart rate pattern look like on a chart?

The OSA pattern — called cyclical variation of heart rate (CVHR) — shows as a repeated sawtooth: CVHR consists of bradycardia during apnea and transient tachycardia at the cessation of apnea. Each cycle includes a drop to 35–45 bpm (the diving reflex response to hypoxia), followed by a spike to 80–95 bpm (the post-arousal sympathetic surge), followed by rapid normalisation. This pattern repeats with every apnea event throughout the night. Toggle to the OSA view in the chart above to see this pattern visually.

Is a sleeping heart rate of 40 bpm too low?

Not necessarily. For trained athletes and highly fit individuals, a resting heart rate of 40–50 bpm is normal and reflects excellent cardiovascular efficiency. During deep slow-wave sleep, the heart rate of a fit adult can legitimately fall to 38–45 bpm without pathology. However, for non-athletes, an unusually slow heart rate could indicate issues such as an electrolyte imbalance, an underactive thyroid, or heart disease. Context matters: if the low heart rate is accompanied by symptoms (dizziness, shortness of breath, fatigue), clinical evaluation is warranted.

Why is my sleeping heart rate higher than usual?

An elevated sleeping heart rate relative to your personal baseline can reflect: accumulated sleep debt (elevated cortisol increases sympathetic tone); illness or infection (immune response elevates HR); overtraining in athletes (parasympathetic recovery is impaired); alcohol consumed close to bedtime (elevates overnight HR through metabolic processing); stress and anxiety (sustains HPA activation into the night); or undiagnosed OSA (the sympathetic surges from apnea events keep baseline nocturnal HR elevated). If consistently elevated without obvious cause, use the Why Am I Tired Tool and consider discussing with your GP.

Can a wearable detect sleep apnea from heart rate patterns?

Wearables can detect features consistent with CVHR — the sawtooth heart rate pattern of OSA — but most consumer devices do not explicitly flag this pattern in their algorithms. A 2026 Frontiers in Physiology review confirmed that CVHR is detectable on standard Holter ECG and correlates with AHI at r = 0.84 in clinical studies. Some premium devices (Withings ScanWatch, certain Garmin models) have FDA-cleared or CE-marked sleep apnea detection features. For a first-pass risk assessment, the Sleep Apnea Risk Screener combines symptom-based screening with risk factors — it does not read your heart rate chart, but provides a validated clinical probability score.

How does heart rate variability (HRV) relate to sleep quality?

Heart rate variability — the beat-to-beat variation in time between heartbeats — is a marker of autonomic nervous system flexibility and parasympathetic tone. HRV is typically higher during nighttime — this evidence supports the concept that overall, sleep is a condition during which vagal activity is dominant. Higher overnight HRV generally indicates better recovery and more restorative sleep. Sleep debt, OSA, stress, and illness all reduce overnight HRV. If your wearable tracks HRV, a declining trend over weeks — even if HR appears normal — is a sensitive early indicator of inadequate recovery.

What should I do if my overnight heart rate chart looks abnormal?

First, identify the pattern using the chart above: elevated baseline (consider sleep debt, stress, illness, alcohol); sawtooth spikes throughout the night (consider OSA); no clear nadir (consider both sleep debt and OSA); irregular rhythm (warrants medical evaluation). Screen for OSA with the Sleep Apnea Risk Screener and calculate your sleep debt at sleepdebtcalc.com. If the pattern includes the sawtooth CVHR, witnessed apnoeas, or accompanied symptoms (morning headache, daytime sleepiness), discuss with a GP for potential home sleep test referral.

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The Bottom Line

A sleep heart rate chart is one of the most information-dense outputs your wearable produces — but only if you know what the patterns mean. The reference data is clear: deep sleep should bring your heart rate to its nightly minimum (40–50 bpm in most adults); REM produces controlled, brief elevations; and a healthy night shows a smooth, stage-correlated curve without the sawtooth spikes that characterise OSA.

The interactive chart above lets you see both patterns and toggle between them. The key patterns to recognise:

1. A smooth declining curve with a clear nadir and 2–4 gentle REM elevations = healthy sleep architecture
2. A sawtooth pattern of repeated bradycardia-tachycardia cycles = CVHR, the OSA signature, with diagnostic correlation (r = 0.84 with AHI) confirmed in 864-patient PSG studies
3. An elevated baseline without clear nadir = sleep debt, stress, OSA, or alcohol — investigate with the tools below

Next steps:

1. Compare your wearable's overnight chart with the normal and OSA patterns in the chart above
2. Screen for OSA with the Sleep Apnea Risk Screener if your pattern resembles the sawtooth
3. Calculate your sleep debt at sleepdebtcalc.com — elevated nocturnal HR from sleep debt is often the most immediately addressable cause of an abnormal chart
4. Use the Sleep Quality Score to track whether interventions are improving your overnight heart rate pattern week over week
5. If your chart shows irregular rhythm, extremely low HR (below 38 bpm, non-athlete), or consistent elevation above 80 bpm during sleep, discuss with your GP

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Tools Referenced in This Article

• Sleep Debt Calculator — Quantify accumulated deficit that may be elevating your nocturnal heart rate
• Sleep Apnea Risk Screener — First-pass OSA risk assessment if your chart shows CVHR-like patterns
• Sleep Quality Score — Track whether sleep interventions are improving your overnight HR pattern
• Why Am I Tired Tool — Structured fatigue and sleep quality analysis when HR chart is elevated
• Sleep Hygiene Checklist — Identify behaviours (late alcohol, late caffeine) that elevate nocturnal HR
• Caffeine Cutoff Calculator — Eliminate caffeine as a confounding cause of elevated overnight HR

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Related Reading

• Sleep Apnea in Women — Health — Why OSA presents differently in women and the cardiac implications
• How Does Sleep Affect Blood Pressure Naturally — Health — The cardiovascular mechanisms linking nocturnal HR patterns to hypertension
• What Happens to Your Body When You Don't Sleep — Health — Systemic physiological consequences including cardiovascular impact
• How to Track Your Sleep Quality at Home — Optimization — Full wearable accuracy guide and non-device tracking system
• Sleep Debt and Headaches — Health — How OSA morning headaches and nocturnal HR spikes share a mechanism
• What Is Sleep Debt — Optimization — Foundational guide to the sleep deficit reflected in elevated nocturnal HR

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References

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13. SleepQuest. What sleep apnea heart rate changes reveal about your heart health. November 2025. https://www.sleepquest.com/sleep-apnea-heart-rate-changes/

14. Nohara R, et al. Dynamics of heart rate and sleep stages in normals and patients with sleep apnea. Neuropsychopharmacology. 2003;28(Suppl 1):S78–S83. doi:10.1038/sj.npp.1300146. https://www.nature.com/articles/1300146

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Disclaimer: This article and the accompanying interactive chart are for educational and informational purposes only and do not constitute medical advice. Heart rate patterns visible on consumer wearables are not clinical diagnostic tools. If you suspect a sleep disorder such as obstructive sleep apnea, or if you have concerns about cardiac arrhythmias or abnormal nocturnal heart rate patterns, consult a qualified healthcare provider or cardiologist. SleepDebtCalc.com tools are designed to support self-awareness and sleep optimisation — they are not diagnostic instruments and should not replace professional medical evaluation.