Your mastery of the shield allows you to fight with it without hindrance.
Prerequisites
Shield Proficiency, Improved Shield Bash, Two-Weapon Fighting, base attack bonus +6.
Benefit
You add your shield’s enhancement bonus to attack and damage rolls made with the shield as if it were a weapon enhancement bonus.
In addition, you do not suffer any Two-Weapon Fighting penalties on attack rolls made with a shield while you are wielding another weapon.