WordNet records no synonym and no antonym for right ventricle. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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 chamber on the right side of the heart that receives venous blood from the right atrium and pumps it into the pulmonary trunk
Synonyms, antonyms and the broader and narrower relations for right ventricle come from Princeton University’s WordNet. Full sources and licences.