A biventricular pacemaker is a special type of pacemaker that helps to treat heart failure.   It gives signals to both sides of the lower chambers of the heart (the right and left ventricles). The therapy provided by biventricular pacemaker is called cardiac resynchronization therapy. By pacing both lower chambers of the heart, cardiac resynchronization therapy helps to coordinate the contraction of heart muscles so that the walls of the heart beat at the same time. Cardiac resynchronization therapy may reduce shortness of breath, improve symptoms and can even prolong life.