Definitions

1. adjective

having or showing a stronger or more vigorous heart; more robust or energetic

“After a few months of regular exercise, John became heartier and more confident.”

2. comparative

more healthy or strong in body

“The heartier of the two brothers was chosen to join the army.”

3. superlative

healthiest or strongest in body

“He was the heartier of the two friends and could finish the marathon in record time.”