Myasthenia gravis is an autoimmune disorder with antibodies to the acetylcholine receptors (Ach R) in skeletal muscles. Myocardial involvement can present as a myocarditis or with arrhythmias. To our knowledge, there is no documentation in the literature of pericardial involvement in myasthenia gravis. We report the presence of pericardial effusion and atrioventricular conduction block in a patient with myasthenia gravis that responded appropriately to immunosuppressive therapy and plasma exchanges.