Study design: 171 patients with persistent AF scheduled for electrical cardioversion are randomised in a double blind, placebo-controlled study. The patients receive tablets of candesartan 8 mg or matching placebo once daily for 3-6 weeks before cardioversion, and candesartan 16 mg or matching placebo once daily for 6 months after cardioversion. The study medication is discontinued if electrical cardioversion is unsuccessful or if AF recurrence is documented. Primary endpoint is recurrence of AF. Clinical, electrocardiographic, echocardiographic and biochemical markers will be analysed.