Despite advances in medical therapy for patients with congestive heart failure, morbidity and mortality remain high. Conventional atrioventricular pacing with a short atrioventricular delay was first introduced as a nonpharmacologic treatment for patients with severe heart failure. Further development of this new therapeutic approach led to biventricular pacing, also known as cardiac resynchronization therapy. Many studies have been published and many are still ongoing. This review summarizes the results reported in randomized trials and focuses on questions that have not yet been answered.