Definition from Wiktionary, the free dictionary
heartbeat (plural heartbeats)
- One pulsation of the heart; especially an irregular one, hence the emotion which causes it.
- The policeman waited for a heartbeat in vain
- He alone gives me such heartbeats
- The rhythm at which a heart pulsates, a cardiac indicator
- If your heartbeat doesn't normalize soon, consult a doctor!
- A driving impulse or vital force.
- Music is the heartbeat of the people.
- A very short space of time; an instant.
- The ambulance arrived in a heartbeat.
- (computing) A periodic signal generated by hardware or software to indicate normal operation or to synchronize other parts of a system.
- (rhythm at which a heart pulsates): pulse
Derived terms 
one pulsation of the heart
the rhythm at which a heart pulsates
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