What does a low HRV actually mean clinically — is it dangerous?

Low HRV in men (below 25–30 ms RMSSD) indicates reduced parasympathetic nervous system activity, the body is spending more time in sympathetic overdrive, and in men without acute illness, sustained low HRV is associated with higher cardiovascular mortality, poor stress recovery, and is often the first measurable wearable signal of subclinical coronary artery disease (Tsuji et al., Circulation, 1996).

The key word is "sustained." A single low HRV reading after poor sleep, a late dinner, a few drinks, or a hard training day is not clinically significant. A trend declining over 4–8 weeks without an obvious cause is a different matter. In my clinical practice, I have evaluated men in their 40s with wearable HRV trends that had been declining for months, assumed by every coach and device algorithm to be a training recovery issue, who turned out to have early subclinical coronary artery disease detectable on a calcium score CT. The HRV was the nervous system's distress signal. The device was right. The interpretation was wrong.

Honesty Scale: Solid (1) for the HRV-cardiovascular mortality association in clinical cohorts. Early (3) for the specific claim that consumer wearable HRV predicts coronary artery disease in asymptomatic men, the correlation exists in research populations but is not validated as a screening tool.

What to do: If your HRV has been below 30 ms consistently for more than 6 weeks, despite adequate sleep and no illness, ask your doctor for a fasting lipid panel with ApoB, hsCRP, fasting insulin, and a discussion of whether a calcium score CT is appropriate.

For the full picture, read Your Whoop Is Worried. Here Is What It Actually Found.