The authors describe a case of a floating thrombus in the left atrium, detected by a 2D echocardiography in a female patient suffering from dilated cardiomyopathy. At the follow-up, it was found that the mass was no longer detected inside the left atrium. This occurrence was not associated to any major embolic phenomena. A transesophageal echocardiographic study revealed the presence of a thrombus in the left atrial appendage.