Research Plan: AF-CHF is a prospective, multicentre clinical trial (100 centres in Canada, the USA, and Europe), that will randomize 1,450 NYHA class II-IV CHF patients with left ventricular ejection fraction >/=35% (NYHA class I patients with prior hospitalization for CHF or ejection fraction </=25% are also eligible) and a history of significant AF (ECG documentation of either one episode lasting >/=6 hours within the past 6 months, or an episode lasting >/=10 minutes within the past 6 months in a patient with prior electrical cardioversion for AF) to one of two treatment strategies: 1) rhythm control with the use of electrical cardioversion if needed combined with antiarrhythmic drug therapy (amiodarone or other class III agents), and additional non-pharmacologic therapy in resistant patients, 2) rate control with the use of drugs (mainly beta-blockers plus digoxin) and/or pacemaker and AV nodal catheter ablation if necessary. The enrollment period will be completed within 2 years with a minimum follow-up of 2 years. Both groups will receive optimal CHF management with ACE inhibitors and beta-blockers. Cardiovascular mortality will be the primary endpoint of the trial. The intention-to-treat approach will be the primary method of analysis. Secondary outcomes are total mortality, hospitalization, stroke, cost of therapy and quality of life. From recent trial data, we anticipate a 18.75% 2-year cardiovascular mortality in the rate control arm and a 25% reduction in cardiovascular mortality in the rhythm control group. Assuming a 2% loss to follow-up, a two-sided alpha level of 0.05 and an annual accrual rate of 750 patients, we calculate that 722 patients per group (rounded total number of 1,450 patients) will be necessary to achieve a power of 0.80 when performing a log-rank test. The Research Centre of the Montreal Heart Institute will be the Coordinating and Methods Centre.