When your heart pulses and pumps blood throughout your body, this is an example of a heartbeat.
When you feel as if the entire summer passed you by in just a single second, this is an example of a time when you might say it went by in a heartbeat.
When the president of a club is the one that keeps the entire club together and functioning, this is an example of a time when the president is the heartbeat.
The baby's heartbeat; a fast heartbeat.
Broadway is the heartbeat of the New York City theater world.
Reappeared in a heartbeat.
I'll be there in a heartbeat.