Some people with heart failure develop abnormal heartbeats, or arrhythmias. Some arrhythmias may reduce how well the heart's lower chambers (ventricles) function. Cardiac Resynchronization Therapy (CRT), also known as biventricular pacing, may be needed. In this procedure, a special pacemaker is used to make the ventricles contract at the same time. This helps the lower heart chambers pump and relax together.