heartbeat
noun.
the rhythmic contraction and expansion of the arteries with each beat of the heart
he could feel the beat of her heart
Synonym: beat, pulsation, pulse
noun.
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
noun.
an animating or vital unifying force
New York is the commercial heartbeat of America