People forget to mention that the second largest Shia (Ja'fari Fiqh) population in the world after Iran is found in Pakistan(around 40-50 million) and although they are extremely quiet against sectarian attacks that happen within the country. An attack on Iran will most definitely rile up their emotions and most likely lead to a civil disturbance, mass protests throughout the country and willing volunteers hoping to help Iran.
I agree with those that have said our Pakistani government won't help Iran, they can't even help ourselves, the best we can do is make sure our land isn't used in anyway by Western Forces as a supply route or for housing their troops.
It's a shame we don't have a government with the testicular fortitude to support Iran wholeheartedly. Strong relations with Iran are absolutely key for our future development and stability it's also essential especially since we already have a poor relationship with Afghanistan and India.