that is a Good News you can attack twice... its called combo rate... you can see an Extra Rounds before it attack right? cool you can attack twice... that is something...
Not exactly, you can combo attack very rarely with a few specific heroes, otherwise if you see the text Extra Turn , that is when your hero has x2 the agility if your opponent, thus he gets to do 2 turns in a row.
That is why people say that agility is the most important stat in PvP, you can get extra turns + you hit first.