This study is a double-blind, randomized, cross-over study of patients with congestive heart failure and a heart rate dependent on a permanent pacemaker. Thus, at all times the heart rate can be maintained at a set rate by adjusting the settings of the pacemaker. Acute and chronic effects of heart rates of 60, 75, and 90 beats per minute will be evaluated by primarily comparing cardiopulmonary exercise tests and radionuclide ventriculography scans.