The website ChineseEtymology.org is phenomenal, and the amount of work put into it is impressive, but I think it’s pretty clear from the precursors that 心 “heart” came from a depiction of a penis, which—let’s face it—is the real source of male emotion.
Sure looks like a penis above. And when you look below, it appears to be various perspectives of the penis. Someone was infatuated.
The precursors of this character 姦 that means “adultery” makes it clear that the heart character 心 really comes from a depiction of a penis (see arrows). See how similar the scripts below resemble those in the previous table.