This gives a blaze 20 health points (because 1 heart = 2 health points). To kill a blaze, you need to inflict 20 points of damage to the blaze.

Zero to one blaze rods are dropped when killed. Blazes have two attacks. When the player is close, the Blaze hits the player for about 2 hearts of damage. If the Blaze has spotted the player, but the player is too far, the Blaze will shoot a fireball at the player which ignites on impact.