It can last for months, in rare cases. You need to take the anti-inflammatory medications ( motrin or aleeve) on a regular basis so that the inflammation has a chance to subside. If this does not occur you can have grave long term consequences, including the rare condition of constrictive pericarditis. You should also have a repeat to check for presence of fluid in the pericardial space, and to make sure the diastolic function of the heart is within normal parameters.