For a few minutes, yes; for good, there is no solid evidence. HRV drops while you sit in a hot sauna and rises as you cool down, and cold water lifts vagal HRV for up to about 15 minutes, but an 8-week trial found regular sauna sessions added nothing to resting HRV beyond what exercise did.
Acute vs lasting effects
Two different questions often get mixed up:
- Acute effect: what HRV does during and right after a session.
- Lasting effect: whether regular sessions raise your resting HRV, the number you track each morning or night.
Saunas and cold water clearly have acute effects. The evidence for lasting effects is thin or negative.
Saunas
During and after a session
Laukkanen and colleagues measured 93 adults, average age 52, with heart risk factors before, during and after one 30-minute sauna at 73 °C (Laukkanen and colleagues, 2019). Heart rate rose in the heat and the vagal part of HRV fell. During the cool-down, high-frequency HRV rose and low-frequency HRV fell. Most HRV measures were back near their starting values after 30 minutes of recovery, and resting heart rate Resting heart rate How many times your heart beats per minute while you are fully at rest. For adults it is usually 60 to 100 beats per minute, and lower in well-trained athletes. More about Resting heart rate at the end was lower than before (68 vs 77 beats a minute).
Over weeks
The best test of a lasting effect is a randomised trial. Lee and colleagues assigned 38 inactive adults, average age 49, each with at least one heart risk factor, to one of three groups for 8 weeks: exercise followed by a 15-minute sauna, exercise alone, or no change (Lee and colleagues, 2025). Exercise improved some HRV measures compared with no change. Adding the sauna made no significant difference to any HRV measure. The trial was small, so a modest benefit cannot be ruled out, but it found no sign of one.
Cold water and cold air
A short, clear rise
A 2024 meta-analysis pooled 24 studies of cold-water immersion and cold-air cryotherapy in healthy people (Jdidi and colleagues, 2024). Cold exposure raised RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next. It mainly reflects vagal activity. More about RMSSD (standardised effect 0.61) and high-frequency power HF power The share of heart rate variability in fast rhythms of 0.15 to 0.40 Hz, the range of normal breathing. It mainly reflects vagal activity when breathing is 9 to 24 breaths a minute. More about HF power (0.46), and slightly lowered heart rate. These changes lasted up to 15 minutes after the cold. Mean blood pressure also rose a little (0.28). The authors noted that responses depended on the person and the cooling method.
Even a cold face is enough. In 13 men, putting the face in cold water for 5 minutes after hard exercise sped up the return of vagal HRV and heart rate recovery compared with sitting quietly (Al Haddad and colleagues, 2010).
After a workout
A 2024 meta-analysis of recovery methods after exercise found that cold-water immersion had a moderate to large effect on RMSSD (g = 0.75), while other physical recovery methods showed no clear effect (Laborde and colleagues, 2024). That points to a faster return of the vagal brake after training. It does not show a higher baseline Baseline Your own usual HRV level and range, built from weeks of readings taken the same way. Comparing a reading with your baseline says more than comparing it with other people. More about Baseline .
Over weeks
The results above are short-term responses, measured within minutes or hours of the cold. We found no trial showing that regular cold plunges raise resting HRV over weeks or months.
What this means for your own data
- Measure away from the heat or cold. A reading taken during or soon after a session mostly shows the session. Keep your daily reading at your usual time.
- Expect a high number after a cold plunge. It is a short-term response, not a fitness gain. If your HRV seems suddenly high, check what you did beforehand.
- For a lasting rise, start with exercise. Regular aerobic exercise has the best evidence. See how to increase HRV.
When to talk to a doctor
Heat and cold both put strain on the heart and blood vessels: heart rate rises in a sauna, and blood pressure rises a little in cold water. Ask your doctor before starting either if you have heart disease, high or low blood pressure, an irregular heartbeat, or you are pregnant. Stop and get help if you feel chest pain, faintness, a racing or uneven heartbeat, or trouble breathing during or after a session.