Inclusion Criteria:

1. Adult Participants, non-HFpEF (25 prospectively enrolled)
   1. Adult controls (>18 years) age, sex, and BMI matched without signs or symptoms of heart failure, confirmed via limited echocardiogram and physical examination.
2. Data retrospectively collected from 25 Adult Participants with HFpEF (≥3 months), age 40-85 years who were enrolled in study 16-001467, defined by:
   1. Signs and symptoms of HF (dyspnea, fatigue), normal left ventricular (LV) EF (≥50% within 12 months of enrollment), and objective evidence of HF as met by at least 1 of the following 4 criteria:
      1. Hospitalization for decompensated HF in the past year but not within the past 30 days;
      2. Invasively-documented elevated pulmonary capillary wedge pressures (PCWP) at rest (>15 mmHg) or with exercise (≥25 mmHg) at catheterization performed in the evaluation of dyspnea;
      3. Elevated NT-proBNP (>400 pg/mL) or BNP (>200 pg/mL);
      4. Echocardiographic evidence of HFpEF based upon current diagnostic guidelines(≥2 of the following: [a] E/e’≥15, [b] ≥moderate left atrial enlargement, [c] PASP >35 mm Hg).

Exclusion Criteria:

1. Adult Participants, non-HFpEF
   1. Signs and symptoms of HF (dyspnea, fatigue), reduced left ventricular (LV) EF (≤50% within 12 months of enrollment), and objective evidence of HF as met by at least 1 of the following 4 criteria:
   2. Hospitalization for decompensated HF in the past year but not within the past 30 days;
   3. Invasively-documented elevated pulmonary capillary wedge pressures (PCWP) at rest (>15 mmHg) or with exercise (≥25 mmHg) at catheterization performed in the evaluation of dyspnea;
   4. Elevated NT-proBNP (>400 pg/mL) or BNP (>200 pg/mL);
   5. Echocardiographic evidence of HFpEF based upon current diagnostic guidelines40 (≥2 of the following: [a] E/e’≥15, [b] ≥moderate left atrial enlargement, [c] PASP >35 mm Hg).
2. Data retrospectively collected from 25 Adult Participants with HFpEF (≥3 months), age 40-85 years who were enrolled in study 16-001467, defined by:
   1. Inability/unwillingness to engage in ET 
   2. Recent (<1 months) HF hospitalization 
   3. Concomitant treatment with organic nitrates or phosphodiesterase 5 inhibitors 
   4. Prior EF <50%, BMI <20 or >50 kg/m2 
   5. Acute coronary syndrome or revascularization within 3 months
   6. Infiltrative, hypertrophic, or radiation-induced cardiomyopathies 
   7. Constrictive pericarditis 
   8. Dyspnea felt to be due to primary lung disease or myocardial ischemia 
   9. Severe anemia (Hgb <8.0) 
   10. Systolic BP <110 mm Hg at consent  
   11. Recent (<30 day) change in diuretics/vasoactive medications 
   12. Significant left-sided valvular heart disease (>mild stenosis, >moderate regurgitation) 
   13. Complex congenital heart disease 
   14. Severe renal (estimated GFR<30) or hepatic disease