Q:

Why there are hearts around my Pokémon? 

I was playing sapphire today as usual but when I sent my zigzagoon to battle I noticed that there are hearts flown around him when it just came out of poke ball not the usual animations of lines or dots.  Why is that? 

A:

Different kinds of Poké Balls have different animations for when they pop open.  In your case, I believe it's either a Nest Ball or a Luxury Ball.