What Constitutes a Good Heart Rate Variability (HRV)
High HRV is generally favorable and indicates robust autonomic nervous system function, good cardiovascular health, and enhanced adaptability to physiological stressors, while low HRV is associated with increased risk of total mortality and cardiovascular disease progression. 1
Understanding HRV as a Health Marker
HRV reflects the fluctuation in time intervals between consecutive heartbeats, providing critical information about the balance between sympathetic and parasympathetic nervous system activity. 1 A healthy heart is not a metronome—the oscillations of a healthy heart are complex and constantly changing, allowing the cardiovascular system to rapidly adjust to sudden physical and psychological challenges. 2
Clinical Significance of High vs. Low HRV
Favorable (High) HRV indicates:
- Lower risk of total mortality and cardiovascular death 1
- Preserved autonomic function, particularly in diabetic patients where it suggests absence of early diabetic neuropathy 1
- Enhanced capacity to adapt to environmental changes and respond appropriately to internal and external stimuli 1
- Adequate stroke volume and cardiac output capacity 1
Unfavorable (Low) HRV indicates:
- Increased risk of total mortality in multiple conditions 1
- Increased risk of cardiovascular disease progression and heart failure 1
- Potential warning of impending cardiac diseases 3
- Enhanced sympathetic and diminished parasympathetic tone, which may predispose to ventricular arrhythmias 4
Measurement Context Matters
There is no single universal "good" HRV number—values must be interpreted based on:
- Recording period length: 24-hour, short-term (~5 min), and ultra-short-term (<5 min) normative values are not interchangeable 2
- Age: HRV naturally decreases with age 5
- Sex: Different baseline values exist between men and women 5
- Cardiovascular fitness level: Higher fitness is associated with higher HRV 5
- Body composition and BMI: These stable factors affect baseline measurements 5
Common HRV Metrics
Time-domain measures quantify the amount of HRV during monitoring periods and include SDNN, rMSSD, and pNN50. 1 Frequency-domain measures calculate signal energy within component bands, with the ratio of low-frequency to high-frequency power providing an approximate indication of sympathetic modulation (though this should be interpreted with caution). 1
Important Clinical Caveats
Short-term HRV has limited data linking it to sudden cardiac death, and its use for sudden cardiac death risk stratification is not currently recommended. 4, 1 The identification of clear limits for differentiation of normal and abnormal results in an individual may be difficult due to marked interindividual variation in the relationship of short-term HRV to parasympathetic effect. 4
Resting tachycardia with high HRV may paradoxically reflect vagal impairment with sympathetic overactivity rather than true autonomic health, and can occur in cardiac disease, poor fitness, obesity, or anemia. 1 This represents a critical pitfall in interpretation.
Improving HRV
Evidence-based methods to optimize HRV include:
- Regular aerobic exercise, which counteracts negative effects of sedentary behavior on autonomic function 1
- Stress reduction practices that activate the parasympathetic nervous system 1
- Addressing sleep disorders and maintaining regular sleep patterns 1
- Reducing alcohol consumption, smoking cessation, blood pressure control, and managing diabetes 1
- Respiratory training with slow, controlled breathing to enhance parasympathetic activity 1