Dronedarone is a new antiarrhythmic agent that has only recently been approved for the therapy of atrial fibrillation (AF). Results regarding a broader spectrum of patients and experience accumulated in clinical practice are still very scarce. Therefore, we prospectively investigated the efficacy and tolerance of dronedarone in a real life setting.The study included 191 patients (85 women) aged 63±9.9years with a history of paroxysmal or persistent AF. Follow-up time was 14.3±4.9months. In patients with persistent AF, sinus rhythm was restored using electrical cardioversion prior to dronedarone administration. Each patient underwent standard ECG on a daily basis during the first 4days of treatment, and on days 7, 30 and 90, resp. After that, the patients had a follow-up visit every three months. Creatinine, creatine kinase, and hepatic enzymes were closely monitored. Clinical history was meticulously taken at multiple follow-up visits. Dronedarone maintained sinus rhythm in 33.5% (95% CI: 27%–40%), and AF recurrence rate was high: 66.5% (95% CI: 60%–73%). Adverse effects occurred in 31.9% (95% CI: 27%–38%) of the patients and necessitated permanent discontinuation of dronedarone in 22% (95% CI: 17%–27%).The results suggest that dronedarone may not be superior to available antiarrhythmic agents and caution against its use as a first line therapy in AF.