The study will aim at investigating novel plasma or imaging biomarkers in patients with acute pericarditis. All participants will be treated according to established clinical recommendations for the diagnosis and treatment of acute pericarditis. Study participants will undergo blood sampling for measurements of plasma biomarkers potentially involved in the pathogenesis of acute pericarditis. Imaging datasets from available imaging tests will be used to quantify imaging biomarkers. Patients will be followed up prospectively for up to 18 months. The prognostic value of plasma and/or imaging biomarkers for development of complications such as atrial fibrillation, pericarditis recurrences, constrictive pericarditis and/or the need to switch to 2nd line treatment will be sought.