-1 for aliasing to heart with or without _(symbol/organ/disambiguation).

Personally, I liked ♥ because it told me exactly what was tagged at a glance, was part of the standard ASCII set (ALT+3), and matched the other card suits – ♦, ♣, and ♠. (There are also other symbols used as tags – ♂, ♀, and ⚥, to only be used when the symbols themselves appear in the picture.) Then someone changed it to <3. True, it's a common smilie, but it breaks the pattern and doesn't match the other symbols. I said nothing because— well, who cares what I think? :\ But I don't really go for heart_(symbol), myself. Why go with two words (or a text picture) when it's simpler for users to just read the very symbol being tagged?

Furthermore, numbers is less important than preventing confusion. To the average user of e621, heart can refer either to the symbol or the organ. That <3 is on thousands of posts while heart_(organ) is on less than 100 posts is irrelevant. Because it's easy to confuse which subject heart might refer to, it's best to clarify.

My suggestions:

Alias: <3 —> ♥ (Matches the other symbols and is more obvious as to what it refers to than heart_(symbol), even if by a little bit.)
Alias: heart —> heart_(disambiguation) (Because different sorts of hearts exist.)
On heart_(disambiguation) page: heart can refer either to ♥ (Press [ALT + Numpad 3] or type <3 ) or to heart_(organ).
___________

To me, it seems the primary issue mentioned in the opening post is the lack of consistency between <3_(whatever) tags and heart_(whatever) tags, so a +1 to fixing that up. I'd suggest shifting anything which is in the shape of or in some way displays the symbol over to ♥_(whatever). Anything that has nothing to do with the symbol goes over to heart_(whatever).