 Congestive heart failure HF is the leading cause of hospitalization among older Americans.1 Approximately half of affected patients have apparently normal systolic function HF with preserved ejection fraction, HFpEF.2-4 In contrast to HF with low EF, there are no proven treatments for HFpEF, due largely to a lack of mechanistic understanding.4 HFpEF patients are typically older, hypertensive and female,2,3 and each of these characteristics is associated with vascular stiffening and dysfunction.5-7 Diastolic abnormalities may contribute to symptoms of exertional intolerance3,8, but non-cardiac limitations have recently been shown to be equally important.9-11 Patients with HFpEF display impaired decreases in mean vascular resistance in response to exercise, significantly limiting performance,9 yet this represents only one component of ventricular afterload. With aging and particularly in HFpEF, pulsatile load due to vascular stiffening and increased wave reflections becomes more magnified.6,12 The latter can be quantified by pulse wave velocity, arterial compliance and carotid augmentation index. These can be determined noninvasively, and while they have been shown to be abnormal in HFpEF patients at rest10,11, little is known about changes in each during exercise stress, or how this might modulate ventricular performance. Recent evidence indicates that endothelial and autonomic dysfunction are present in HFpEF9, but it is not known how these abnormalities might limit ventricular-vascular function with exercise. The primary objective of this proposal is to compare resting and exercise-induced changes in vascular function in patients with HFpEF and age-matched controls, to determine how these factors may affect exercise performance and cardiovascular reserve function. 