Average Sleeping Heart Rate for a 6-Month-Old Infant
The average sleeping heart rate for a healthy 6-month-old infant is approximately 119 beats per minute during quiet sleep, with a normal range of 94–150 beats per minute (2nd–98th percentile). 1
Normal Heart Rate Ranges During Sleep
- Mean sleeping heart rate at 6 months: 119.4 beats per minute during quiet sleep 2
- Normal range (5th–95th percentile): 93.7–149.9 beats per minute during quiet sleep 1
- Active sleep (REM) heart rate: Slightly higher at approximately 123.8 beats per minute 3
The heart rate during quiet sleep is consistently lower than during active (REM) sleep at all ages during infancy. 3
Age-Related Context
Heart rate decreases progressively during the first year of life. At 6 months, infants show a marked decrease from earlier months:
- 1 month: Mean sleeping heart rate of 138.6 beats per minute 3
- 3 months: Mean sleeping heart rate drops to 118 beats per minute 3
- 6 months: Mean sleeping heart rate stabilizes around 119 beats per minute 2, 1
This physiologic decline reflects maturation of the autonomic nervous system and cardiovascular development. 3
Clinical Considerations
Heart rates as low as 70 beats per minute during quiet sleep are acceptable if there are no signs of circulatory compromise (pallor, mottling, cyanosis) and the infant responds appropriately to activity. 4
Sustained heart rates near or above 150 beats per minute during sleep may warrant further evaluation for underlying conditions such as fever, infection, anemia, pain, dehydration, or cardiac abnormalities. 5
Measurement Recommendations
- Heart rate should be assessed when the infant is quietly sleeping, not agitated or crying, as activity significantly elevates heart rate 5
- Vital signs should be documented as stable for 12 hours when assessing overall infant health 4
- Heart rate shows normal physiologic variation with feeding, sleep state transitions, and defecation due to changes in vagal tone 5