Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Pericarditis ?
    ### Response:
    In many cases, the cause of pericarditis (both acute and chronic) is unknown.
                
Viral infections are likely a common cause of pericarditis, although the virus may never be found. Pericarditis often occurs after a respiratory infection. Bacterial, fungal, and other infections also can cause pericarditis.
    