heartbeat

(noun) the rhythmic contraction and expansion of the arteries with each beat of the heart. Synonyms: pulse, pulsation, beat. Examples: "He could feel the beat of her heart."

(noun) a very short time (as the time it takes the eye to blink or the heart to beat). Synonyms: blink of an eye, flash, instant, jiffy, split second, trice, twinkling, wink, New York minute. Examples: "If i had the chance i'd do it in a flash."

(noun) an animating or vital unifying force. Examples: "New york is the commercial heartbeat of america."