From the Knit Picks Website:

This is another traditional pattern adapted to socks. None of “my guys” like hearts on their socks so only one width is provided for this one-circular needle, toe-up pattern, but you can change the needle size up or down.

Why a toe-up pattern, besides the usual advantages to toe-up knitting, like being able to try the sock on as you knit for a better fit? It’s a small detail, but I think that hearts just look better when they come to a point at the bottom rather than having “wings.” Knitting toe up solves the problem.