Depending on the game you are playing they would re-deal. In the game of Texas Holdem poker however, they would take the extra card and it would be used as the first burn card.
The deal should be cancelled with every player returning their cards. The dealer should then reshuffle and deal again correctly with the proper number of cards to each player. This may be frustrating if you receive a very good hand when the dealer has made a mistake like that but that is the only fair way to correct it.
I suppose that depends on what game you're playing, but generally you just call for a misdeal and repeat the process from the beginning. No need to have a heart attack, just fix the problem.
