Malignant pericardial effusion is a frequent complication in primary mediastinal and pleural malignancies. As a first manifestation of a malignant tumour, however, it is rare. With cardiac tamponade the likelihood of malignancy increases. We report a life-threatening cardiac tamponade as the primary clinical presentation of a pericardial mesothelioma. Pericardiocentesis resolved the acute symptoms, followed by surgical pericardial fenestration. Oncologic therapy is evidently indicated. All mesotheliomas carry a poor prognosis.