The levels stack.

If we look at Eldritch Heritage it says:

Select one sorcerer bloodline. You must have Skill focus in the class skill that bloodline grants to a sorcerer at 1st level (for example, Heal for the celestial bloodline). This bloodline cannot be a bloodline you already have. You gain the first-level bloodline power for the selected bloodline. For purposes of using that power, treat your sorcerer level as equal to your character level – 2, even if you have levels in sorcerer. You do not gain any of the other bloodline abilities.

If we then look at the Arcane Bloodline, it states:

Arcane Bond (Su): At 1st level, you gain an arcane bond, as a wizard equal to your sorcerer level. Your sorcerer levels stack with any wizard levels you possess when determining the powers of your familiar or bonded object. This ability does not allow you to have both a familiar and a bonded item.

This means that your effective sorcerer levels gained from Eldritch Heritage stack with any wizard levels you have for determining the abilities of your Arcane Bond essentially.

So a level 11 wizard with Elritch Heritage (Arcane) that had selected a Familiar for their arcane bond, would determine the abilities of their Familiar as if they were level 20.