Why this app exists

[marekkowalczyk]

I built this because I needed it.

I have heart failure with reduced ejection fraction (HFrEF). Slow breathing at resonance frequency — around 6 breaths per minute — is one of the few non-pharmacological interventions shown to improve cardiac vagal tone and baroreflex sensitivity. The evidence is solid: Bernardi et al. demonstrated measurable improvements in oxygen saturation and exercise tolerance in CHF patients, with effects visible after a single session.

The problem was consistency. I needed a daily habit tool, not a meditation app. No accounts, no guided audio, no subscription. Just: open terminal, start breathing, follow the bar.

The safety constraints are not theoretical. Breath retention raises intrathoracic pressure and can trigger arrhythmia. Rapid breathing mobilises catecholamines — the opposite of what a failing heart needs. These are hard-coded rejections, not settings.

If you are a cardiac patient, please talk to your cardiologist before starting any breathing practice. This app is not a medical device.

If you have HRV biofeedback hardware, the README includes a protocol for finding your individual resonance frequency. If you don't, the 6 bpm default is well-supported by the literature.

— Marek