cross heart

Old English heorte "heart; breast, soul, spirit, will, desire; courage; mind, intellect," from Proto-Germanic *khertan- (cf. Old Saxon herta, Old Frisian herte, Old Norse hjarta, Dutch hart, Old High German herza, German Herz, Gothic hairto), from PIE *kerd- "heart" (cf. Greek kardia, Latin cor, Old Irish cride, Welsh craidd, Hittite kir, Lithuanian širdis, Russian serdce "heart," Breton kreiz "middle," Old Church Slavonic sreda "middle").

Spelling with -ea- is c.1500, reflecting what then was a long vowel, and remained when pronunciation shifted. Most of the figurative senses were present in Old English, including "intellect, memory," now only in by heart. Heart attack attested from 1875; heart disease is from 1864. The card game hearts is so called from 1886.