Radiofrequency catheter ablation (RFCA) at the ostium of the pulmonary veins can potentially cure atrial fibrillation. Left-sided ablation procedures may carry a risk of thrombo-embolic events. Emboli from intracardiac thrombus originate from the left atrial appendage (LAA) in a substantial number of patients. The presence of spontaneous echo contrast in the left atrium (LA) and LAA peak emptying flow < or = 20 cm/s are also significantly related to thrombo-embolic events. Evaluation of the anatomy of the LA and LAA prior to left-sided procedures is therefore mandatory. Intracardiac echocardiography (ICE) appears an ideal technique to obtain this information during the RFCA-procedure. In the current report, we report on the use of ICE detecting a thrombus in the LAA in a patient planned to undergo RFCA of pulmonary veins for atrial fibrillation.