What heart rate is dangerous? No single number. Symptoms decide.

Call 911 now, at any number

• Chest pain, pressure or tightness.
• Fainting, or feeling about to faint.
• Trouble breathing or shortness of breath.
• Confusion, or a fast heartbeat with hot skin after being in the heat.
• A racing or pounding heartbeat that keeps going and does not settle.

Do not drive yourself. This list does not change with the number on your screen.

The numbers doctors use at rest

• Above 100 BPM at rest: called tachycardia (fast heart rate).
• Below 60 BPM at rest: called bradycardia (slow heart rate). People who are young or physically fit may normally sit lower.
• Well-trained athletes: 40–60 BPM is listed as normal.
• Children: run higher, and the range depends on age. See heart rate by age.

These are names for a range, not verdicts. A number above 100 while you walk upstairs is not tachycardia in the sense a doctor means, because “at rest” is part of the definition.

Is too low more dangerous than too high?

Neither is safer by rule. A low number with dizziness, fainting, unusual tiredness or confusion needs a doctor. A low number in someone who feels well and trains a lot usually does not. See low resting heart rate.

Book a regular appointment if

• Your resting pulse stays above 100 on most mornings. In CDC data that is higher than about 98 in 100 adults.
• Your awake resting pulse stays below 50 and you do not train hard. That is lower than about 97 in 100 adults.
• Your pulse often feels irregular, or skips or flutters.
• Palpitations keep coming back, last longer than a few minutes, or you have a heart condition or a family history of heart problems.
• Your usual resting number has changed a lot over weeks and you do not know why.

Bring what you have. Seven mornings of readings from the 7-morning check say more than one number.

Usually not a reason to worry on its own

• A higher number while walking, or after a scare, that settles within minutes.
• A lower number while asleep.
• Day-to-day changes of a few beats.
• A faster pulse with a fever, or in the heat, that settles as those pass and comes with no other symptom.

If you are unsure, it is always fine to ask.

What to tell the doctor

• Your resting readings, with the time of each.
• What you were doing when a high or low number showed up.
• How you felt: light-headed, short of breath, a fluttering feeling.
• Your medicines and supplements.
• How you measured: by hand, phone app or watch.