HRV is the most information-dense biomarker available from consumer wearables — a single overnight measurement that reflects autonomic nervous system balance, stress load, sleep quality, and cognitive readiness. Most people treat it as a fitness recovery metric. This article covers the more valuable application: HRV as a daily cognitive performance readiness indicator. The neurovisceral integration model directly links resting HRV to PFC function. Alcohol is the strongest HRV suppressor in most people’s lives. Resonance frequency breathing is the fastest available intervention. 26 months of Oura Ring + Creyos data confirms the predictive relationship.