study diet is no longer available to match with the previous participants.

The purpose of this study is to examine how dietary changes affect the heart and blood vessels in patients with hypertension (high blod pressure) who have a condition called 'heart failure with preserved ejection fraction" (HFPEF). This condition is also known as "diastolic heart failure" or "heart failure with normal ejection fraction", and occurs even though the heart's pumping function is normal.

In an earlier study, the investigators found that patients with HFPEF who ate a special diet for three weeks had improved blood pressure control and lower levels of blood chemicals that may damage the heart and blood vessels. The eating plan in the study was based on the DASH diet, also known as the Dietary Approaches to Stop Hypertension diet. This plan is rich in fruits, vegetables, and low-fat dairy, and is recommended to decrease blood pressure in patients with hypertension. Current medical guidelines also recommend that both patients with hypertension and those with heart failure should decrease their dietary salt intake.

The diets that patients will eat in this study are the DASH/sodium-restricted (DASH/SRD) diet as well as a control diet based on the average reported diet collected using Food Frequency Questionnaires during our pilot study. Patients will be randomized to one diet for three weeks and then crossover to the other diet for three weeks. Patients will then be asked to eat the DASH/sodium-restricted diet on their own at home with dietary support for an additional eight weeks.

In this study, the main goal is to confirm the findings of our earlier study. The investigators would also like to understand how the DASH/SRD changes the function of the heart and blood vessels during exercise and the activity of genes that could be involved in HFPEF.

Inclusion Criteria:

• Symptoms and/or signs of HFPEF in the past 12 months
• Most recent LVEF ≥ 50% (contrast ventriculography, echocardiography, nuclear scintigraphy)
• Diastolic dysfunction on previous echocardiogram/catheterization or evidence of abnormal neurohormonal activation (B-type natriuretic peptide (BNP) ≥ 100 pg/ml)
• History of systemic hypertension
• Willing to adhere to provided diet

Exclusion Criteria:

• NYHA Class IV heart failure symptoms
• Hospitalization for decompensated HF within past one month
• Uncontrolled hypertension (seated SBP ≥ 180 or DBP ≥ 110) at rest, on current antihypertensive regimen
• Changes in medical regimen for heart disease or hypertension within past 1 month, except diuretic dose adjustment (within past 1 week)
• Previous LVEF < 40%
• Primary exercise limitation due to severe pulmonary disease
• Uninterpretable echocardiographic windows
• Worse than moderate mitral or aortic stenosis or insufficiency.
• Baseline serum potassium level > 5.0 mmol/L or prior history of potassium > 6.0
• Serum calcium/phosphorus product > 50 at baseline
• Severe renal insufficiency (current estimated GFR < 30 ml/min)
• Severe anemia (Hgb < 9 g/dL)
• Severely uncontrolled diabetes mellitus (Hgb A1C > 10%)
• Non-hypertension related cause of HFPEF (e.g. amyloidosis, sarcoidosis, constrictive pericardial syndromes, primary hypertrophic or restrictive cardiomyopathy)
• Primary right ventricular failure
• Myocardial infarction or unstable angina, including new or worsening anginal syndrome, within the past three months
• Uncontrolled arrhythmia (including non rate-controlled atrial fibrillation)
• Terminal illness expected to result in death within six months
• Psychiatric disorder or dementia with potential to compromise dietary adherence