Depends does player B have a card that beats any of the cards on the board therfore making a higher flush. Easiest way I think I can illustrate this is ;
Board ;
A

K

Q

3

7
Player A: A

K
Player B: A

4
Player B wins because he has a higher flush player A has Ace high flush with a 3 of hearts, where Player B has Ace high flush with four of hearts Higher hearts.
hope this helps.
I Know some of the folks here have slammed the Milwaukees Best commercials for the WSOP but there is a great example there of one player having the heart when the other didn't and it was the difference between winning the pot and not (it actually dealt with a hand that Greg Raymer was playing).
There was a post the same time mine was so hope this helps