This method Removes local role assignments and inherits role assignments from the parent object.
If a list has some items that are using unique permission you can reset the permissions back to list using this method.
SPListItem.ResetRoleInheritance();
Thanks to the SDK
mk:@MSITStore:C:\Program%20Files%20(x86)\Microsoft%20SDKs\SharePoint%202010\SP2010SDK.chm::/html/b814e6a6-8b27-5d27-e6c3-2fbc5fc1e284.htm