Introduction: Mitral stenosis is mainly caused by rheu-matoid arthritis, although the incidence of this etiology is decreasing and the age at which it becomes symp-tomatic varies very much. Moreover, when finding an intracardiac mass, we should always do a differential diagnosis, firstly with pathologic situations and then with normal cardiac structures.

Methods: We present the case of a 72 years old woman who presented at the emergency room for worsening severe dyspnea at rest up to orthopnea and important weakness. Summing clinical exam and history of the patient we thought at a cardiac decompensation in the context of an infectious pulmonary process (bibasal subcrepitant crackles, right basal crepitant crackles, moderate leg swelling). Electrocardiocram shows AFi (documented persistent atrial fibrillation) with rapid vetricular response. The aspect of thoracic radiography suggests right basal alveolar condensation, but also in-terstitial opacities and cardiomegaly. Laboratory tests revealed important inflamatory syndrome (leukocyto-sis with neutrophilia, high level of inflamatory mar-kers). Echocardiographic examination describes tetracavity dilation with moderate systolic dysfunction of left ventricle and the mitral valve has typical changes for rheumatic disease with severe stenosis and regurgi-tation; furthermore, in the right atrium (RA) we iden-tify a phyliphorm hypermobile structure attached to the interatrial septum with the length of 2.7 cm.

Results: We decide, next to perform a transesophageal echocardiography (TEE) for better characterisation of the intra-atrial mass and to exclude a possible throm-bus or vegetation. TEE confirms the rheumatic etiology of mitral disease with both cusps severely affected and commissural fusion and round orifice of opening; at the confluence of coronary sinus with RA a thin, mo-bile, phyliphorm is seen, which probably is a longer Thebesius valve (aspect not typical for thrombus or vegetation). According to the new diagnosis, we con-tinue the anticoagulation with acenocoumarol for the prevention of thromboembolic events and also adequa-ted treatment for the infectious pulmonary process and subsequent acute heart failure. It is considered in the near future the percutaneous balloon valvotomy.

Conclusions: In conclusion, it was an episode of cardi-ac decompensation started by a pneumonia at a patient with valvular and arrhythmia- induced cardiopathy. It is also important the differential diagnosis of an intra RA structure, with is established by TEE, being only an incidentaloma (particular Thebesius valve), but also it is revealed the rheumatic etiology of mitral valve di-sease. It is also rare to encounter such a severe valvular disease that remains asymptomatic so much time. In times of observing less and less rheumatic affection of valves, it is important to know the typical aspect of it and also for all intracardiac masses, an exhaustive di-fferential diagnosis should be done, excluding the life-threatening situations.