The object of the game is to achieve the fewest points. Multiple games are usually played, the scores being retained between games.
The game is meant for four people; other numbers commonly play by removing the two of clubs and possibly other two's from the deck prior to dealing so that the number of cards in the deck is divisible by the number of players.
Game
Play as basic /Whist. At the end of the game, each player examines the cards they won. They score 1 point for each card which has the suit of Hearts, and 13 points for the Queen of Spades. All other cards score 0 points. Iff a single player obtains all the cards worth a nonzero amount of points in the deck during the game, they score zero points and everyone else scores the total point count in the deck each (26 in the basic game), for that game only.
Variations
Microsoft's Hearts programme has made famous the variation of passing three cards to someone else before the game starts. Usually, games are played in sets of four, with each player passing to the left in the first game, to the right in the second, across (four players are assumed) in the third and not passing at all in the fourth. All cards are hidden.
Microsoft's Hearts also requires the first card played to be the 2 of Clubs, and disallows Hearts from being led until one has been played. (Hearts are then said to have 'broken').
(PeterTaylor) An exception is made for the case where you have to lead and only have hearts.
There is a variation where each heart is worth its face value (Jack is 10, Queen is 11, King is 12, Ace is 13), the King of Spades is worth 7 points and the Ace of Spades is worth 5. There is also another with Hearts at face value, and the Queen of spades worth 20 or so.
Hearts can also be played with two decks and lots of players, perhaps the most fun variation being cancellation Hearts, where if the same card is played twice to a trick then it doesn't count for the purposes of deciding who won the trick. If all cards are cancelled then the person who led won the trick.
Black Maria is supposed to be a three person game (although it works well for any number) - one addition is that after the deal, the remaining odd cards are placed face down in the pot - and are won by whoever takes the first trick. This way there is a penalty for playing all of your high cards on the first trick.
The version of Black Maria that I have played takes each heart as 1 point and the Queen as 13, but King and Ace of spades also score 10 and 7 respectively. I've never seen that other part mentioned above...
Same in mine - mine also had breaking hearts (see below). --Angoel
I was interested to learn that the rule "You may not lead hearts until someone has won a trick containing hearts" (Known as 'breaking hearts') is not actually a part of the official game, but is another variant. A good one though.
To be honest, I think it is part of the official rules, but someone else listed it as being part of the microsoft variant, so I thought I'd better make it consistent with that variant. There is certainly no one gold standard set of rules out there.
Nope, according to my book of rules, both are listed as separate variants.
Finally (from me at least) comes the 'invented at about 4am' variant: Cheat-Maria. Cards are played face down, with each person announcing what they are playing. A correct challenge forces the cheater to take the trick (regardless of who normally should win it) and an incorrect challenge forces the challenger to take it. This leads, of course, to everyone after those players to discard as many hearts as they can. Shooting the moon is obviously almost impossible in this variant (a challenge can always prevent it) Tricks can be turned face up after each play, or only at the end of the game, whichever is felt to produce the most laughter.