Erdheim-Chester disease (ECD) is a rare non-Langerhans histiocytic disorder. We report a 76-years-old man who suffered a cardiac tamponade secondary to ECD. A pericardial window was made and during the operation the surgeons observed that the myocardium was diffusely infiltrated. Twenty-eight months before, ECD was clinically diagnosed and prednisone and methotrexate were prescribed. Due to disease progression which culminated in the cardiac tamponade, methotrexate was changed to sirolimus aiming to obtain plasma levels between 5-8 ng/ml. This treatment stabilized his cardiac function allowing a survival of 52 months after its initiation, with fewer side effects.Erdheim-Chester disease (ECD) is a rare non-Langerhans histiocytic disorder. We report a 76-years-old man who suffered a cardiac tamponade secondary to ECD. A pericardial window was made and during the operation the surgeons observed that the myocardium was diffusely infiltrated. Twenty-eight months before, ECD was clinically diagnosed and prednisone and methotrexate were prescribed. Due to disease progression which culminated in the cardiac tamponade, methotrexate was changed to sirolimus aiming to obtain plasma levels between 5-8 ng/ml. This treatment stabilized his cardiac function allowing a survival of 52 months after its initiation, with fewer side effects.