Play proceeds clockwise. You must follow suit if you can.; If you cannot follow, you may play any card — this is how penalty cards get discarded onto other players.; The highest card of the suit led wins the trick, and that player leads the next.
Why people argue about this
People often assume that playing a trick with a card from another suit automatically disqualifies it as invalid, which isn't true according to Hearts rules. The confusion arises because they misinterpret the rule allowing you to play any card if you can’t follow suit, not realizing this means including cards of other suits in your play.
