Heart rate 166 on an adult - what does it mean?
A resting heart rate of 166 bpm is very high. During hard exercise it can be expected (see the training table below) — at rest, a pulse this fast needs urgent medical attention.
Where 166 bpm sits on the adult scale
- Very low
- Low (bradycardia)
- Slightly low
- Normal
- Elevated (tachycardia)
- High
- Very high
What a resting pulse of 166 means
At rest, a sudden racing heartbeat of 166 bpm is usually not ordinary sinus rhythm. Typical causes are supraventricular tachycardia (SVT), atrial flutter or fibrillation, and — less often but more dangerous — ventricular tachycardia.
Also double-check the reading: wrist devices can lock onto your movement cadence during exercise and report it as heart rate.
Ranges apply to adults and children aged 10 and older, measured at rest (American Heart Association). By the numbers: at 166 bpm the heart beats about every 0.36 seconds — roughly 239,040 beats a day.
166 bpm during exercise
During exercise a higher pulse is expected. This table shows which training zone 166 bpm corresponds to, based on the common estimate of maximum heart rate (220 minus age). Individual maximums can differ by 10–20 bpm.
| Age | Est. max (220 − age) | 166 bpm is | Training zone |
|---|---|---|---|
| 20 | 200 bpm | 83% of max | Zone 4 · Hard |
| 30 | 190 bpm | 87% of max | Zone 4 · Hard |
| 40 | 180 bpm | 92% of max | Zone 5 · Maximum |
| 50 | 170 bpm | 98% of max | Zone 5 · Maximum |
| 60 | 160 bpm | 104% of max | above estimated max |
| 70 | 150 bpm | 111% of max | above estimated max |
How the zones work: Heart Rate Zones: The 5 Training Zones by Age.
For a reliable resting value, sit quietly for five minutes first and average a few mornings: Resting Heart Rate: What It Says About Your Health. You can also measure by tapping along on the start page.
Check another reading
Nearby values
Measured on a child instead? See heart rate 166 in a child.
Sources: American Heart Association: All About Heart Rate · MedlinePlus: Pulse · ACSM position stand on exercise intensity (2011)
This page explains a single reading in general terms. It is not a diagnosis. Heart rate alone cannot tell whether the rhythm is regular or whether the heart is healthy — if you are worried, talk to a doctor.