Aim: Transesophageal echocardiography (TEE) guided early cardioversion (CV) in conjunction with short-term anticoagulation has been shown to be safe, and an alternative to prolonged conventional anticoagulation therapy. Recently, low molecular weight heparins (LMWHs) have been used successfully as an alternative to standart heparin therapy obviating the need for hospitalization and APTT monitoring. The aim of this study was to determine the efficacy and safety of TEE guided early cardioversion in conjunction with short-term LMWH use in patients with nonvalvular atrial fibrillation (NVAF). Methods and results: The study group consisted of 172 consecutive patients with NVAF. Before TEE, 90 patients received LMWH (Dalteparin 2x5.000u SC) and 82 patients received standart heparin (UFH) (5.000u IV bolus followed by IV infusion to raise APTT to 1.5 times control). TEE was performed and left atrium and left atrial appendix was searched thoroughly for the presence of thrombus. One patients from each group was excluded due to detection of left atrial thrombus by TEE. Immediately after TEE, CV was attempted and warfarin was initiated. All patients received warfarin for one month after CV. In the LMWH group, 89 of 88 patients (98.9%) was successfully cardioverted. CV was successful in patients 97.5% in the UFH group. None of the patients experienced thromboembolic events during the four weeks after CV. Conclusion: TEE guided early CV in conjunction with short-term LMWH treatment is as safe as UFH for the prevention of the thromboembolic events after CV.