Origin and history of heart

name applied to several types of flowering plant, 1690s; see bleeding (adj.) + heart (n.).

In the American English sense of "person liberally and excessively sympathetic" (especially toward those the speaker or writer deems not to deserve it) is attested by 1936 in the work of popular conservative newspaper columnist Westbrook Pegler (1894-1969), who first used it in reference to his own feelings about the Republican Party but by 1938 regularly deployed it against the Roosevelt administration and also as a modifier (bleeding-heart liberal) in his "Fair Enough" column: 

And I question the humanitarianism of any professional or semi-pro bleeding heart who clamors that not a single person must be allowed to hunger, but would stall the entire legislative program in a fight to jam through a law intended, at the most optimistic figure, to save 14 lives a year. ["Fair Enough," in Freemont (Ohio) Messenger, Jan. 8, 1938]

Bleeding in a figurative sense of "generous" is attested from late 16c., and the notion of one's heart bleeding as a figure of emotional anguish is from late 14c.; the exact image here may be the "bleeding heart of Jesus."

c. 1300, usually plural, bowels, "human organs of the abdominal cavity," from late 14c. specifically as "human intestines," from Old French boele "intestines, bowels, innards" (12c., Modern French boyau), from Medieval Latin botellus "small intestine," originally "sausage," diminutive of botulus "sausage," a word borrowed from Oscan-Umbrian.

The transferred sense of "the viscera as the seat of emotions" is from late 14c.; especially "inner parts as the seat of pity or kindness," hence "tenderness, compassion." Greek splankhnon (from the same PIE root as spleen) was a word for the principal internal organs, which also were felt in ancient times to be the seat of various emotions. Greek poets, from Aeschylus down, regarded the bowels as the seat of the more violent passions such as anger and love, but by the Hebrews they were seen as the seat of tender affections, especially kindness, benevolence, and compassion.

Splankhnon was used in Septuagint to translate a Hebrew word, and thence early Bibles in English rendered it in its literal sense as bowels, which thus acquired in English a secondary meaning of "pity, compassion" (late 14c.). But in later editions the word often was translated as heart. Bowel movement is attested by 1874.