Striking with both of your weapons simultaneously, you can use them to deliver devastating wounds.
Benefit: If you hit an opponent with both your primary hand and your off-hand weapon, you deal an additional 1d10 points of damage plus 1-1/2 times your Strength modifier. You can only deal this additional damage once each round.
*Note: It has been stated in an FAQ that this feat should function as the Universal Monster Ability Rend. In this case, the damage amount is the 1d10 +1-1/2 times your Strength+Other modifiers, like Power Attack, Piranha Strike, sneak attack (if both triggering attacks were eligible for it as well), etc. Weapon damage modifiers, such as enhancements, those specifically stated to be weapon damage bonuses, like divine favor, etc. do not apply to the feat’s bonus damage.
Pathfinder RPG Core Rulebook. Copyright 2009, Paizo Publishing, LLC; Author: Jason Bulmahn, based on material by Jonathan Tweet, Monte Cook, and Skip Williams.