A 25-year-old woman presented with progressively worsening shortness of breath, which was attributed to cardiac tamponade caused by pericardial effusion. Urgent pericardiocentesis revealed haemorrhagic fluid, which continued to accumulate after the procedure. A repeat echocardiogram after pericardiocentesis showed dilatation of the right ventricle and severe pulmonary hypertension. Subsequent computed tomography revealed a massive pulmonary embolism in the right lung (Figure) and multiple small emboli in the left lung, while cytological examination of pericardial and pleural fluid showed adenocarcinomatous cells from a primary lung cancer.