Without further evaluating you, I cannot tell you the cause of your pericardial effusion. For our other readers, a pericardial effusion is a collection of fluid in the sac around the heart. There are several different causes of pericardial effusions. The most common is a viral infection caused pericarditis. It is usually treated with anti-inflammatory medications, such as ibuprofen, and usually (but not always) self-resolves. However, there are other reasons, as well, including bacterial, fungal, or tuberculosis infection, cancer, and autoimmune disease, such as lupus. Considering the fact that you had some ankle swelling and depending on how long you have had this effusion, it may be more appropriate for you to have further evaluation for either cancer or autoimmune disease.
The effusion by itself should not cause problems, especially if it is small. The times that there are problems include if there is rapid enlargement of the effusion such that the heart cannot adequately fill with blood, or there is an active infection around the heart, or if there is inflammation that leaves a calcified rim around the heart. Again, this will require close follow-up by your cardiologist and further evaluation as to the cause of your effusion. The treatment is based upon the underlying cause of the effusion, although if there is a rapid rise in the effusion amount, a pericardiocentesis, or sterilely placing a needle through the chest wall into the pericardial sac to drain off the fluid, may need to be performed. This is not performed for small effusions, though.