(1) The heart is a large involuntary muscle in the chest cavity.
(2) The heart has its own timer: it takes advice, but not orders, from the central nervous system.
(3) Heart is where the home is.
(4) If you go back far enough, heart is related to core, courage, cordial, and cardiac (but not to curd, curt, or courteous): the hypothesized Proto-Indo-European root is kerd-. The Germanic languages, you will recall, changed an intial 'c' into 'h', which is why a Latin unicorn has a cornus, but an English one has a horn.
(5) The meanings of English heart used to include "memory." We have forgotten this, mostly. Except that we still learn things "by heart."