Follow the led suit
If you hold the suit led, you must play that suit. The highest card of the led suit wins the trick. A card of a different suit does not win it.
When hearts are broken
In many versions, a heart must first be discarded by someone unable to follow suit before hearts can be led. A player holding only hearts may have an exception. First-trick restrictions vary.
Check the current trick
Check the led suit before playing. A card that cannot be selected may be restricted by follow-suit or first-trick rules; inspect the game help before assuming it is unresponsive.