A case of a 65-year-old patient, showing dyspnea to strains and right side pain as main symptoms of an approximately 8 cm cyst in the pericardium. The physical, biochemical and electrocardiographic examinations did not evince any changes. The results from the thoracic radiography, CT scan and echocardiogram suggested pericardial cyst. Based on those clinical evidences, the patient was submitted to a thoracotomy in the right side thoracic region and a complete excision of the mediastinal mass was performed, with complete remission of the symptoms.