They are more heavily and most heavily.
While the comparatives heavier and heaviest may be used as adverbs, they do so as forms of the word 'heavy' where it is used (rarely) as an adverb.
Comparative Form- more heavilySuperlative Form- most heavily
The comparative is greater and the superlative is greatest.
comparative straighter and the superlative the straightest
Comparative - better Superlative - best
Comparative - cuter Superlative - cutest
Comparative Form- more heavilySuperlative Form- most heavily
more heavily, most heavily
comparative : purer superlative : purest
Comparative: older Superlative: oldest
Dative; Early Comparative; Earlier Superlative; Earliest
The comparative and superlativeforms of grand are: Comparative: grander Superlative: grandest
comparative - merrier superlative - merriest
comparative = sadder superlative = saddest
Comparative: shallower Superlative: shallowest
The comparative is "stricter" and the superlative is "strictest".
The comparative is greater and the superlative is greatest.
"More heavily" is a comparative. "Most heavily" would be a superlative.