Slow, rhythmic breathing at roughly six breaths per minute brings the respiratory rhythm into resonance with the baroreflex — the feedback loop that regulates blood pressure beat-to-beat. Resonance maximises heart rate variability and trains the vagus nerve, the main conduit of the parasympathetic (rest-and-digest) nervous system.

It’s not a wellness theory. It’s been measured in laboratories since the 1990s, refined into a clinical protocol by Paul Lehrer and Evgeny Vaschillo, and replicated across populations from Olympic athletes to PTSD patients.

The breath pacer in this app is the same protocol — quieter, on your phone.

Read the full science

“Resonance frequency breathing maximizes heart rate variability via baroreflex resonance, with documented effects on autonomic balance and stress recovery.”

Lehrer & Gevirtz, 2014 · Heart rate variability biofeedback: how and why does it work?Frontiers in Psychology, 5:756

“Five minutes of cyclic sighing per day reduced state anxiety and improved positive affect more than equivalent mindfulness meditation.”

Balban et al., 2023 · Brief structured respiration practices enhance mood and reduce physiological arousalCell Reports Medicine, 4(1)

Programs

Or follow a journey.

Three multi-day programs that build HRV progressively, wind you down for sleep, or wake you up with focused energy. Daily-locked, two-tap entry, no commitment.

7 days

HRV Bootcamp

Progressive resonance breathing that ramps from 6 BPM down to 5 BPM as your nervous system catches on. Each day builds on the last. Built for the first week.

Resonance · 3 → 10 min

5 nights

Sleep Wind-Down

Evening-focused 4-7-8 and extended-exhale protocols that pull you into parasympathetic before bed. The body learns the pattern after the first few nights.

4-7-8 · Extended Exhale

5 mornings

Morning Activation

Box breathing for focus, then 7 BPM resonance for alert calm. Designed for the first ten minutes of your day, before the inbox.

Box · Resonance 7 BPM

Free forever to breathe. Programs are part of Pro.

Apple Watch · Apple Health

Built around your wearable.

HRV Breathe reads your most recent SDNN sample from Apple Health before and after every session. The Watch app delivers the same pacer on your wrist — no phone needed.

Your HRV data never leaves your device. There is no server to compromise, no account to create, no analytics on your physiological data. We can’t see it because we never receive it.

See it on the Watch

Inhale

Common questions

The honest answers.

Do I need an Apple Watch?

No. The app works on iPhone alone — you can breathe, build a streak, follow programs, and use the Physiological Sigh exercise without any wearable. You need an Apple Watch (or a third-party device that writes HRV to Apple Health, like Oura, Whoop, Garmin, Fitbit, or Polar) to see your HRV change after sessions. That's the only feature gated on a wearable.

What is HRV, in one sentence?

Heart rate variability is the small, beat-to-beat variation in the time between heartbeats — a number that goes up when your nervous system is flexible and recovered, and down when it's stressed or fatigued.

Is breathwork safe? Are there contraindications?

Slow resonance breathing at 5–7 breaths per minute is safe for the overwhelming majority of people. If you have a history of severe panic, fainting at hyperventilation, a heart condition under treatment, or you are pregnant, talk to your clinician first. We do not use breath retention beyond what's in standard techniques like Box and 4-7-8, and we never recommend extended breath-holds.

How quickly will I see results?

You'll feel a difference in the first session — that's the within-session HRV change the app surfaces on the completion screen. Raising your resting HRV is slower: most users see a measurable upward trend at 7–14 days of daily practice, with the largest gains in the first six weeks. The literature reports +10 to +25% baseline HRV improvement over 8–10 weeks of consistent resonance training.

Will it work if I have anxiety or panic?

Slow breathing is one of the most evidence-backed interventions for everyday anxiety. For acute panic in the moment, 4-7-8 is usually our recommendation. For ongoing anxiety regulation, build a daily resonance habit. We're not a treatment for clinical anxiety disorders — we're a tool that pairs well with one.

What's free vs Pro?

All four breathing techniques, the pacer, your daily streak, HRV before/after readings, and the Physiological Sigh are free forever. Pro ($4.99/mo, $29.99/yr with a 7-day trial, or $99.99 lifetime) adds the multi-day guided programs, HRV trend insights, all ambient soundscapes, smart reminders, and share cards.

Where does my data go?

Your HRV data never leaves your device. We read it from Apple Health, use it to compute your before/after delta, and store the result locally. There is no server, no account, no analytics on your physiological data. We can't see it because we never receive it.

Why is there no Android version?

Because Apple Health + Apple Watch are the only mature mobile HRV pipeline we trust. Google Fit's HRV story is partial, and the Wear OS HRV ecosystem is fragmented. We'd rather do one platform well than two badly. If you'd like to be notified when that changes, leave your email in the footer.

Three minutes.
One measurable change.

Download on the App Store See the science first

Free forever. iPhone & Apple Watch. No account.

Breathe smarter.See the difference.

Every session ends with a number.

Four ways to breathe.Each one does something different.

Resonance

Box breathing

4-7-8

Extended exhale

At six breaths per minute, your nervous system listens.