Pericarditis is an inflammation of the pericardium, the thin sac-like membrane surrounding the heart. This condition can cause chest pain, which may feel sharp or stabbing, and can worsen with deep breathing or lying down. Other symptoms may include fever, fatigue, and a feeling of pressure in the chest. The causes of pericarditis can vary and include infections, autoimmune diseases, or previous heart surgery. Diagnosis typically involves a physical examination, imaging tests like an echocardiogram, and sometimes blood tests. Treatment often includes medications to reduce inflammation and relieve pain.