"heartbeat" in the noun sense
1. pulse, pulsation, heartbeat, beat
the rhythmic contraction and expansion of the arteries with each beat of the heart
"he could feel the beat of her heart"
2. blink of an eye, flash, heartbeat, instant, jiffy, split second, trice, twinkling, wink, New York minute
a very short time (as the time it takes the eye to blink or the heart to beat
"if I had the chance I'd do it in a flash"
an animating or vital unifying force
"New York is the commercial heartbeat of America"
Source: WordNet® (An amazing lexical database of English)
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