Free lesson. Runs in your browser. Nothing is uploaded.
Heartbeat Lab: see your heart rate and heart rate variability live
Connect a Bluetooth chest strap and watch the anatomical heart beat at your measured rate. Then follow the pacer and observe whether your beat-interval timing changes. The three-minute comparison puts a 60-second resting baseline beside 120 seconds of paced breathing on your own signal. Responses differ, and a short before-and-after comparison cannot show what caused a difference.
Choose the signal source
No source yet. A chest strap sends your own beat intervals; the demonstration is a simulated signal and is not your physiology.
Anatomical heart at the measured rate
Waiting for a source
Teaching animation of a heart cycle. Its playback speed follows the most recent beat interval. It is not imaging of your heart and shows no cardiac morphology.
Live readouts
Heart rate-- beats per minute
Last beat interval-- ms between beats
rMSSD estimate, last 60 seconds-- ms, illustrative
Beats received0 since start
What this rMSSD estimate is and is notThe root mean square of successive differences between the beat intervals your strap sent in the last 60 seconds, after dropping intervals outside 300 to 2000 ms. It is a short illustrative estimate, not a controlled five-minute ECG measurement, and no evidence grade is assigned to it. The registry statement that carries Grade A is specifically: five-minute ECG rMSSD, under controlled conditions, as an index of cardiac vagal activity. Do not read this number as a measure of overall vagal function, recovery, or health. No single population-wide rMSSD value is appropriate for judging your health from this short consumer-sensor reading; published reference ranges depend on age, sex, and measurement conditions. Compare yourself to yourself.
Breathing pacer at six breaths per minute
Four seconds in through the nose, six seconds out. Follow the orb. Near six breaths per minute the breath-linked rise and fall of heart rate tends to swing widest; watch whether your readouts show it.
Pacer off
Watch the heart rate readout: in many people it rises slightly on each inhale and falls on each exhale. A breath-linked swing of that kind is what respiratory sinus arrhythmia looks like; this lab has no respiration signal, so it cannot confirm that your breathing produced the swing you see. The registry statement is Grade B: slow paced breathing can increase heart-rate oscillation and support self-regulation; durable outcomes vary, and so does how calm anyone feels.
Three-minute comparison: 60-second resting baseline, then 120 seconds of paced breathing
Sit still and breathe normally for 60 seconds. The pacer then starts by itself for 120 seconds. At the end you see both rMSSD estimates side by side. Start it after the readouts are moving. This is an uncontrolled comparison on one occasion; it cannot show what caused any difference.
Not started
Phase
Duration
Beats used
Heart rate range
rMSSD estimate
Resting baseline
60 s
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Paced breathing, 6 per minute
120 s
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Beat-to-beat intervals over the last 60 seconds
Each point is one beat. Height is the time since the previous beat in milliseconds; left is 60 seconds ago, right is now. A wide, regular wave that follows your breathing is the pattern slow breathing often produces. A flat line means the timing is not changing beat to beat.
Which sensors and browsers work
Sensors
Expected to work, not yet verified by Zencora: chest straps that broadcast the standard Bluetooth Heart Rate Service with beat intervals, such as Polar H10, H9, and H7; Garmin HRM-Dual and HRM-Pro; Wahoo TICKR; Coospo H6 and H808S.
Wet the electrodes and wear the strap snug under the chest. Make sure no other app holds the strap.
Wrist watches and rings usually do not broadcast beat intervals and will not show rMSSD here.
Browsers
Live strap: Chrome or Edge on Windows, Mac, Linux, ChromeOS, and Android. Live-strap mode is a beta: Zencora has tested the packet parser on synthetic packets but has not yet completed a physical-strap validation. If it fails for you, use the demonstration and tell us what happened.
Safari, iPhone, and iPad: the demonstration only. Apple does not ship Web Bluetooth in Safari.
If no beat arrives for five seconds the heart stops, the readouts clear, any running comparison is stopped, and the status says so. The lab never substitutes a simulated beat for a missing live one.
What this lab does not do
It does not diagnose, screen, or treat anything, and it is not a medical device. A single reading is not a verdict about your heart or your health, and a before-and-after comparison does not show what caused a change.
It does not compare you to other people. Published rMSSD reference ranges depend on age, sex, and measurement conditions and do not apply to a short consumer-sensor reading; the comparison this lab offers is you against your own baseline.
It does not store or send data. Readings live in this browser tab and are gone when you close it. Write down the two rMSSD values if you want to keep them.
It does not stimulate the vagus nerve, and it does not measure breathing. It displays your beat-interval timing while a breathing pacer is shown; without a respiration signal or a controlled comparison it cannot establish that breathing caused a change.
Stop and rest if you feel light-headed while pacing. Anyone with a heart rhythm condition or a pacemaker should ask their clinician before paced-breathing practice.