Introduction: The aim of the study was to evaluate the prevalence of the silent intracardiac thrombosis in patients with acute decompensated heart failure and sinus rhythm, without anticoagulation therapy, hospitalized in the internal medicine department of an emergency hospital. Methods: A retrospective study of medical records was performed for 116 patients with acute decompensated heart failure, consecutively hospitalized between January and December 2013. In all patients clinical exam, laboratory tests, chest X-Ray, transthoracic echocardiography, abdominal ultrasound, ECG were performed in the first 24 hours after admission. Exclusion criteria: the presence of atrial fibrillation, valve prosthesis, intracardiac device. Results: 12 patients were diagnosed with intracardiac thrombosis (10.34%). The mean age of the patients was 60.83 ± 4.88 years. 3 patients were women, 9 patients were men. Left ventricular thrombus was found in 3 patients (25%), left atrial thrombus in 7 patients (58.33%), right atrial thrombus in 2 patients (16.66%). Mean left ventricular ejection fraction was 34.75 ± 3.29%, mean left ventricular end-diastolic diameter was 58.75 ± 2.75 mm, and mean left atrium diameter was 47.66 ± 2.11 mm. Ventricular thrombosis was associated with apical aneurysm in patients with silent ischemia. Left atrial thrombosis was associated with mitral annular calcifications. Right atrial thrombosis was associated with dilated cardiomyopathy or Budd-Chiari syndrome. Conclusions: Silent intracardiac thrombosis in emergency hospitalized patients had a high prevalence. Left ventricular aneurysm, dilated cardiomyopathy and valvular calcifications were the most common causes of intracardiac thrombosis in our patients with acute decompensated heart failure and sinus rhythm.