A cardiology patient developed a minimal terminal app for resonance breathing training at 6 breaths per minute. The single Python file requires no dependencies beyond Python's standard library, making it frictionless to install and run. Created specifically for macOS using afplay for audio cues, the tool follows clinical protocols for improving cardiac vagal tone through paced breathing.

The app enforces safety constraints critical for cardiac patients: no breath retention to avoid Valsalva risk, minimum 8-second cycles to prevent hyperventilation, and exhale ratios not exceeding double the inhale. Users can immediately exit with q or Ctrl+C, with terminal restoration guaranteed even during crashes. The MIT-licensed project provides a simple command-line interface without app store requirements.

Resonance breathing amplifies respiratory sinus arrhythmia, strengthening vagal outflow and improving baroreflex sensitivity. Individual frequencies between 4.5-6.5 bpm can be found using a chest-strap HRV monitor and the provided protocol. Though designed for HFrEF patients, the tool offers a free, evidence-based approach to autonomic balance training without subscriptions or accounts.