Heart failure is a major health problem in Canada. Recent advances in medical and device therapy have helped to reduce the morbidity and mortality of patients with this problem. Among these treatments, cardiac resynchronization therapy (CRT) has very recently been shown to be effective to improve functional class, quality of life and exercise tolerance of the patients with the most severe symptoms of heart failure and a prolonged duration of the QRS on the 12-lead Electrocardiography (ECG).