What's the adjective for heartiest? Here's the word you're looking for.
Included below are past participle and present participle forms for the
verbs heart and hearten which may be used as adjectives within certain contexts.
“Above 6,000 rogues and vagabonds were arrested in different parts of the kingdom and shipped off with the most heartless disregard for their actual necessities during so long a passage.”
“I thought, of course, if the judgment day had come, I should be no longer a slave in the power of a heartless tyrant.”
“And that to believe otherwise is to be a heartless, right-wing reactionary.”