heartbeat

noun

1. 1

   an animating or vital unifying force

   New York is the commercial heartbeat of America

2. 2

   the rhythmic contraction and expansion of the arteries with each beat of the heart

   he could feel the beat of her heart

3. 3

   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