A male patient in his 20s with a medical history of common variable immunodeficiency disorder, non-compliant with therapy, presented to the emergency department with respiratory distress and severe hypoxaemia. Chest radiography demonstrated extensive bilateral infiltrates and an increased cardiothoracic ratio. urine antigen test was positive. ECG demonstrated diffuse ST-segment elevation. An arterial line was placed and demonstrated pulsus paradoxus. Transthoracic echocardiography revealed an extensive pericardial effusion, with echocardiographic signs of cardiac tamponade. Emergency subxiphoid pericardiocentesis was performed with an initial drainage of 750 mL of purulent fluid consistent with pyopericardium. Immediate haemodynamic improvement was observed. The patient required a second pericardiocentesis for drainage of a relapsing pericardial effusion. The course was complicated by effusive-constrictive pericarditis requiring anterior interphrenic pericardiectomy. Treatment with intravenous immunoglobulin and antibiotics led to a complete recovery.© BMJ Publishing Group Limited 2023. No commercial re-use. See rights and permissions. Published by BMJ.