Breath–Heart Biofeedback
Breathe with the circle while your phone camera reads your pulse — and watch your heart rate rise on each inhale and fall on each exhale. That’s your vagus nerve, live. This is ONDA in miniature.
⚠ Live biofeedback demo, not a medical device. Use a phone; the heart-rate trace is a rough camera estimate and will jitter. The breath–heart effect shows best with a still finger and slow breathing. All processing is on-device; nothing is recorded or uploaded.
- 1. Use a phone. Tap start, allow the camera.
- 2. Gently cover the rear camera + flash with a fingertip; hold still.
- 3. Breathe with the circle and watch the green heart-rate line ride the breath wave.
The rise-and-fall of heart rate with breathing is respiratory sinus arrhythmia (RSA) — a normal, healthy sign of vagal activity, strongest at slow breathing. Educational biofeedback demo, not medical advice; the camera trace is a rough estimate and will be noisy. Processed on-device only.
This is the 30-second version. ONDA is the real one.
A fingertip on a camera hints at the breath–heart connection. ONDA Life reads it continuously and accurately against your live HRV — so you can train calm and watch your nervous system respond.
Download ONDA Life on the App Store →Sources & methodology
This combines two of our other tools into the single demonstration that best captures what ONDA does. The phone camera reads your pulse from a fingertip over the rear camera and flash (contact PPG), detecting each beat in real time to plot your instantaneous heart rate. At the same time, the pacer guides your breathing — and as you breathe, you should see your heart rate climb on the inhale and drop on the exhale. That oscillation is respiratory sinus arrhythmia (RSA): a real, direct window on your vagus nerve, strongest when you breathe slowly at around six breaths a minute (Yasuma & Hayano 2004; Lehrer & Gevirtz 2014). It is a live biofeedback demo, not a medical device — camera beat-detection is noisy and the trace will jitter (Coppetti 2017), and the RSA pattern shows up most clearly with a still finger, a good signal and slow breathing. Everything runs on your device; no video is recorded or uploaded.
- [1] Yasuma F, Hayano J (2004). Respiratory sinus arrhythmia: why does the heartbeat synchronize with respiratory rhythm?. Chest, 125(2):683–690.
The phenomenon this tool shows — heart rate rises on inspiration and falls on expiration (RSA), an index of vagal tone.
- [2] Lehrer PM, Gevirtz R (2014). Heart rate variability biofeedback: how and why does it work?. Frontiers in Psychology, 5:756.
Why slow breathing at ~6/min maximises this heart-rate oscillation (resonance) — the core of HRV biofeedback.
- [3] Coppetti T, Brauchlin A, Müggler S, et al. (2017). Accuracy of smartphone apps for heart rate measurement. European Journal of Preventive Cardiology, 24(12):1287–1293.
Why the camera heart-rate trace is a rough estimate, not a measurement — smartphone PPG accuracy varies widely.
Common questions
What am I supposed to see?
Your heart rate rising as you breathe in and falling as you breathe out — the green heart-rate line oscillating in time with the breathing wave. That’s respiratory sinus arrhythmia (RSA): your vagus nerve modulating your heartbeat with each breath. It’s most obvious when you breathe slowly (~6/min) with a steady finger on the camera.
Why does my heart rate go up when I inhale?
On the inhale, vagal "braking" on the heart eases off and the heart speeds up slightly; on the exhale, vagal tone returns and it slows. This rhythmic change — RSA — is a normal, healthy sign of an active parasympathetic nervous system (Yasuma & Hayano 2004), and bigger swings generally mean better vagal tone.
Why slow breathing at about 6 a minute?
Around six breaths per minute is the cardiovascular resonance frequency, where the heart-rate oscillation driven by breathing is largest and HRV peaks (Lehrer & Gevirtz 2014). It’s the rate used in HRV biofeedback. Faster breathing produces smaller, harder-to-see swings.
How accurate is the heart-rate trace?
It’s a rough, real-time estimate from your phone camera, and it will jitter — smartphone PPG accuracy varies a lot (Coppetti 2017), and detecting individual beats from a camera is harder than averaging heart rate. Treat this as a biofeedback demo to feel the breath–heart connection, not as precise medical data.
Is my camera feed private?
Yes. All processing happens live in your browser on your device. No image or video is recorded, saved or uploaded — frames are analysed for the pulse signal and immediately discarded, and the camera turns off when you stop.