Thank you very much for all your help.
Pericardial effusion originates in the obstruction of venous or lymphatic drainage from the heart. Common causes of pericardial effusion include heart failure, renal insufficiency, infection (bacterial, viral, or tuberculous), neoplasm (carcinoma of lung or breast, or lymphoma), and injury (from trauma or myocardial infarction).
You didn't mention what tests were given. May require a CT scan or MR of the pericardial anatomy (outer sac covering the heart) to properly characterize and delineate pericardial lesions such as pericardial thickening, pericardial mass, etc.
"When an effusion is secondary to malignancy, an irregularly thickened pericardium or pericardial nodularity may be depicted on MR images. Because most or all of the chest is evaluated during CT or MR imaging of the pericardium, associated abnormalities in the mediastinum and lungs also may be detected during the examination.
Although pericardial masses are often detected initially with echocardiography, CT and MR imaging are useful for the further evaluation of these masses. CT attenuation or MR signal intensity characteristics, degree of contrast enhancement, and presence or absence of blood flow on cine MR images can help differentiate among pericardial masses. CT and MR imaging also can be used to accurately define the site and extent of masses".
I've heard of tumors in the heart (myxomas) but they are usually inside the heart, little dangly things that can cause some symptoms. I don't know what tumors on top of the heart are called.