This will be a double blind randomized crossover study of patients with congestive heart failure and a heart rate dependent upon 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. The effect of heart rate will be determined by measuring ejection fraction by nuclear ventriculography, six minute walk distance, and peak oxygen consumption on a maximal exercise test.