Which matters more, HRV or resting heart rate?

Use them together. HRV and resting heart rate usually move in opposite directions and tell the same story from two sides. A low HRV with a sleeping heart rate a few beats above your usual is a clearer signal than either one on its own.

HRV gets the attention because it swings more. But the two are tied. A slower heart leaves more time between beats for the gaps to vary, and a faster heart leaves less. Some of that link is plain arithmetic, and some is the same nerve slowing the heart and adding the swing.

Resting heart rate is also the easier number to measure well. In a 2025 overnight test against a chest strap, the average error for resting heart rate was 3 percent or less on Oura, WHOOP and Polar. For HRV it ran from 6 to 16 percent across five devices. In a 2024 test, the authors called Apple Watch’s resting heart rate relatively accurate, while its HRV came in about 8 ms low.

What do the combinations mean?

The evidence

Drinks move both at once. In 20,968 WHOOP members, a night with one drink more than usual, against one less, came with a sleeping heart rate 2.8 beats higher in women and 2.4 in men, and HRV 3.8 and 3.3 ms lower. In Fitbit data from 2,745 people with COVID-19, heart rate and breathing rate went up during illness and HRV went down.

Weekly averages of both beat single days. In 10 runners over nine weeks, the weekly average of resting heart rate and of HRV each lined up closely with how much their 10 km time improved. The values from single days barely did.

So check your sleeping heart rate whenever HRV surprises you, and judge both on their 7-day averages.