This study will be a three period crossover study. Patients initially will be randomly assigned to be paced at a rate of 60, 75, or 90 BPM for 2 consecutive months. Patients with rate responsive pacemakers will be set at an upper limit of 20 beats above their assigned rate. At the end of this period, patients will have end point measurements obtained and then will be randomized to one of the other heart rates for another 2 consecutive months. Following repeat end point measurements at the end of this period, patients will then be randomized to the final heart rate for 2 consecutive months with repeat measurements at the end.