Pericardial effusion is an extremely rare expression of hyperthyroidism. We report a case of a patient with Graves’ disease who developed a sanguineous pericardial effusion. Our patient had been hospitalized for retrosternal chest pain and dyspnea. She underwent pericardiocentesis resulting in 700 ml of blood. The pericardial fluid’s cytology and culture were negative. Besides, thyroid hormone markers were progressively normalized using antithyroid drugs .Thus the pericardial effusion resolved without recurrence.