>Stat changes are swapped with the opponent. ~ Pokémon DB
>Switches user's stat increases with opponent. ~ Serebii
Heart Swap switches stat boosts with the opponent, not actual base stats.
The difference between Heart Swap and Guard Swap/Power Swap is that Heart Swap exchanges stat boosts with your opponent, while Guard and Power Swap switch you Defensive stats with your Offensive stats and vice versa.