A dangerous heart rate for a child with a fever depends on the child's age and the degree of fever. Generally, a child's heart rate increases about 10 to 12 beats per minute for every 1°C (1.8°F) rise in body temperature. Tachycardia (a very high heart rate) can be concerning, especially if the heart rate significantly exceeds age-appropriate normal ranges even after accounting for fever.
Normal and Dangerous Heart Rates by Age (without fever)
- Newborn: 100 to 180 bpm
- 1 to 11 months: 90 to 160 bpm
- 1 to 2 years: 85 to 150 bpm
- 2 to 4 years: up to about 140 bpm
- Older children and teenagers have lower normal ranges.
Heart Rate Increase with Fever
- Expect about a 10-12 bpm increase per 1°C rise in temperature.
- For example, a 3°C fever might cause a 30-36 bpm increase normally.
Dangerous Heart Rate Thresholds by Age (with or without fever)
- Less than 12 months: >160 bpm is concerning
- 12-24 months: >150 bpm is concerning
- 2-4 years: >140 bpm is concerning
- For newborns, a resting heart rate above 180–200 bpm is considered dangerous.
- In teenagers, a resting heart rate persistently above 100 bpm at rest may be a threat.
When to be concerned
- If the heart rate is extraordinarily high beyond what fever explains (e.g., above these thresholds after adjusting for temperature).
- If there are symptoms such as dizziness, extreme irritability, fainting, or signs of poor circulation.
- When tachycardia is accompanied by signs of respiratory distress or poor hydration.
In summary, a heart rate above these age-specific thresholds adjusted for fever can be dangerous and warrants prompt medical evaluation to exclude serious illness or complications such as sepsis.
