Pericarditis is inflammation of the pericardium (the fibrous sac surrounding the heart). Symptoms typically include sudden onset of sharp chest pain. The pain may also be felt in the shoulders, neck, or back. It is typically better sitting up and worse with lying down or breathing deep. Other symptoms may include fever, weakness, palpitations, and shortness of breath. Occasionally onset of symptoms is gradual. The cause of pericarditis is believed to be most often due to a viral infection. Other causes include bacterial infections such as tuberculosis, uremic pericarditis, following a heart attack, cancer, autoimmune disorders, and chest trauma. The cause often remains unknown. Diagnosis is based on the chest pain, a pericardial rub, specific electrocardiogram (ECG) changes, and fluid around the heart. Other conditions that may produce similar symptoms include a heart attack.