Heart failure is a progressive disease that decreases the pumping action of the heart. This may cause a backup of fluid in the heart and may result in heart beat changes. When there are changes in the heart beat sometimes an implantable heart device is used to control the rate and rhythm of the heart beat. The purpose of the REVERSE clinical trial is to determine whether pacing in both the left and right ventricles using Cardiac Resynchronization Therapy (CRT) can help slow the progression of heart failure in people who have mild or previous symptoms and poor heart pumping function. This kind of therapy has previously been shown to reduce symptoms and improve exercise capacity in people with more advanced forms of heart failure.