heart has 30 distinct synonyms spread across 7 of its 10 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the hollow muscular organ located behind the sternum and between the lungs; its rhythmic contractions move the blood through the body
“he stood still, his heart thumping wildly”
an area that is approximately central within some larger region
“it is in the center of town”
the choicest or most essential or most vital part of some idea or experience
“the gist of the prosecutor's argument”
an inclination or tendency of a certain kind
“he had a change of heart”
a plane figure with rounded sides curving inward at the top and intersecting at the bottom; conventionally used on playing cards and valentines
“he drew a heart and called it a valentine”
a firm rather dry variety meat (usually beef or veal)
“a five-pound beef heart will serve six”
a playing card in the major suit that has one or more red hearts on it
“he led the queen of hearts”
Synonyms, antonyms and the broader and narrower relations for heart come from Princeton University’s WordNet. Full sources and licences.