Under the Constitution, the Vice President serves as President of the Senate. He may vote in the Senate in the case of a tie, but is not required to. The President Pro Tempore (and others designated by him) usually perform these duties during the Vice President's frequent absences from the Senate.
the person who takes over the Presidency in case of illness or death of the President. The Vice President also acts as president of the Senate, over which he presides. He or she may not vote in the Senate, except to break a tie. Presidential candidates often choose running mates to attract support from voters otherwise disinclined to vote for them. For most of American history, the role of the Vice President was very limited. Under the presidencies of Carter, Reagan and Clifton, however, the Vice President has been given more responsibilities.