Pericardial mesothelioma, light micrograph. Primary mesotheliomas of the heart arise from the pericardium. There should be no concurrent pleural involvement. Association with asbestos exposure is not as strong as that with pleural mesotheliomas. The morphology of pericardial mesotheliomas is similar to those seen elsewhere. They are composed of atypical, pleomorphic cells with an infiltrative growth pattern within the pericardium. This image shows tumour cells with papillary architecture on the pericardial surface.