As much as the heart can hold or contain; as much as a person wants or can endure.
Late 16th century. From heart + -ful.
Characterized by deep emotion or sincerity of expression; genuine, sincere, heartfelt. Of an emotion: deeply or acutely felt; intense.
Late Middle English; earliest use found in Robert Mannyng (d. c1338), poet and historian. From heart + -ful.