To answer your question regarding prognosis may depend on the underlying cause. In about 90% of acute pericarditis, the underlying cause is unknown.
Other common causes include infection, kidney failure, heart attack (MI). There can be a malignancy, damage from radiation, and direct injury.
Thanks for your question, and if you have any further questions or comments you are welcome to respond. Take care, and i wish you the best going forward,
Ken