Why Infants Have a Faster Heart Rate Than Adults
A heart rate of 140 would be alarming in a resting adult — and is completely normal in a three-month-old. The reasons lie in the size of the heart, the needs of a fast-growing body and the way the nervous system matures.
Small heart, small stroke volume
The amount of blood the heart moves per minute (cardiac output) is heart rate times stroke volume — the amount pumped per beat. A newborn's heart pumps only a few milliliters per beat. The immature heart muscle also has less ability to increase its stroke volume, so a baby's heart raises its output mainly by beating faster.
A body with high demands
Relative to their size, babies have a much higher metabolic rate than adults: they grow quickly, have a larger surface area for their weight and lose heat easily. Their tissues need more oxygen per kilogram, which means more blood flow per kilogram — delivered by a faster heart.
The nervous system's brake develops later
The vagus nerve acts as the heart's brake. Its influence grows through infancy and childhood, which is one reason the resting heart rate falls steadily with age. The same principle holds across the animal kingdom: small mammals have fast hearts (a mouse around 500 bpm), large ones slow hearts (an elephant around 30 bpm).
How the heart rate falls with age
| Age | Normal resting heart rate |
|---|---|
| Newborn (0–1 month) | 100–190 bpm* |
| Infant (1–11 months) | 80–160 bpm |
| Toddler (1–2 years) | 80–130 bpm |
| Preschool (3–4 years) | 80–120 bpm |
| Child (5–6 years) | 75–115 bpm |
| Child (7–9 years) | 70–110 bpm |
| 10 years and older | 60–100 bpm |
Source: NIH MedlinePlus; ranges for an awake, calm child.
* Newborns: MedlinePlus lists 70–190 bpm. We use 100 as the lower limit, because in a newborn a heart rate below 100 needs prompt medical assessment (newborn resuscitation guidance treats under 100 as bradycardia).
What is not normal
A fast heart rate is expected in babies, but a few patterns need medical attention:
- A calm baby's heart rate consistently above the range for their age, or above 220 bpm at any time.
- A slow heart rate — below the normal range (in a newborn, below 100), and especially below 60 bpm in a baby who seems unwell (an emergency).
- Signs that the heart is struggling: poor feeding, sweating during feeds, fast breathing, poor weight gain, pale or bluish skin.
Your pediatrician checks your baby's heart rate at routine visits. If you are worried between visits, call them. See also How to Measure a Baby's Heart Rate.
Sources: MedlinePlus: Pulse · AHA 2020 guidelines, neonatal resuscitation
Check a heart rate
Related guides
- How to Measure a Baby's Heart Rate
- Fast, Slow or Irregular Heart Rate in a Child
- The Human Heart Rate: What Is Normal and What Changes It
- Resting Heart Rate: What It Says About Your Health
This page offers general information, not medical advice. If your heart rate worries you, please talk to a doctor. In an emergency, call 911 (US) or your local emergency number.