Heart failure is a clinical syndrome where the heart is unable to pump enough blood to satisfy the organism's metabolic needs. Heart failure has become a major clinical and public health problem with approximately 300,000 Canadians being affected. Atrial fibrillation is a rhythm disorder in which the upper chambers of the heart (the atria) are paralyzed by continuous electrical activity. Some of the continuous chaotic electrical activity in the atria travels to the lower cavities of the heart (the ventricles) causing then to beat irregularly and very rapidly. It is the most frequent cardiac arrhythmia, affecting 5% of individuals 65 years and older and it is associated with an increased risk of stroke. Both conditions (heart failure and atrial fibrillation) often co-exist in the same patient. Heart failure promotes atrial fibrillation and atrial fibrillation aggravates heart failure. The Atrial Fibrillation and Congestive Heart Failure (AF-CHF) trial is investigating whether preservation of normal cardiac rhythm influences mortality and morbidity. The AF-CHF study began in 2001 and 1,378 patients have been enrolled from 123 participating centres, in North America, South America, Europe, and Israel. The results of this trial which are expected in October 2007, will improve decision-making for the physician and will provide useful information to healthcare organizations responsible for the care of heart failure patients.