The number of heartbeats per unit time is usually expressed in minutes. The normal heart rate is usually between 60 and 100 beats per minute.
Different age groups
The number of normal heartbeats is defined as follows: more than this number is called tachycardia and less than that is called bradycardia. It becomes:
In infants (1 to 30 days): 140 to 160 beats per minute
Infants (1 to 3 years old): 120 to 140 beats per minute
Child (3 to 12 years old): 100 to 120 beats per minute
Adults: 60 to 100 beats per minute