WordNet records no synonym and no antonym for rheumatic heart disease. 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.
heart disease caused by recurrent episodes of rheumatic fever; characterized by changes in the myocardium or scarring of the heart valves that reduce the power of the heart to pump blood
Synonyms, antonyms and the broader and narrower relations for rheumatic heart disease come from Princeton University’s WordNet. Full sources and licences.