All heroes are free.

Competitive balance is Dota's crown jewel, and to ensure everyone is playing on an even field, the core content of the game—like the vast pool of heroes—is available to all players. Fans can collect cosmetics for heroes and fun add-ons for the world they inhabit, but everything you need to play is already included before you join your first match.

"...totally free to play in the way

we wish all free-to-play games could be"

–IGN