Inclusion Criteria:

Group 1: HFpEF-CKD-will consist of 30 subjects with:

* Ejection fraction of equal or greater than 55%; and
* Evidence of increased LV filling pressures, including at least 2 of the following: average septal-lateral E/e' ratio ≥ 15; tricuspid regurgitation (TR) peak velocity \> 2:8 m/s;
* Left atrial volume index \>34mL/m\^2 assessed by echocardiography; and
* Previous diagnosis of HF with New York Heart Association (NYHA) functional class II-III symptoms on chronic diuretic therapy; and
* CKD defined as glomerular filtration rate (eGFR) of 15-80 mL/min/1.73 m\^2 as estimated by the Modification of Diet in Renal Disease equation. Subject needs to be on stable dose of chronic diuretic for at least 4 weeks prior to study and maintained on the same dose for the duration of the study. In addition to the exclusion criteria listed below, to ensure a more homogenous group of subjects, we will exclude subjects with Diabetes or BMI \> 35 (because endogenous natriuretic peptide levels are low in obese subjects).

Group 2: HFpEF-EI-will consist of 30 subjects with:

* Ejection fraction of equal or greater than 55%; and
* Previous invasive determination of normal pulmonary capillary wedge pressure (\< 15 mmHg) at rest and ≥ 25 mmHg during exercise; and
* New York Heart Association (NYHA) functional class II-III symptoms; and
* Glomerular filtration rate (eGFR) of \> 50 mL/min/1.73 m\^2 as estimated by the Modification of Diet in Renal Disease equation. In addition to the exclusion criteria listed below, to ensure a more homogenous group of subjects, we will exclude subjects with Diabetes or BMI\>35 (because endogenous natriuretic peptide levels are low in obese subjects).

Exclusion Criteria:

* Body mass index \> 35.
* Blood pressure \< 100/60 or \> 180/100 mmHg.
* Diabetes.
* Myocardial infarction within 6 months of screening.
* Unstable angina within 6 months of screening, or any evidence of myocardial ischemia.
* Significant valvular heart diseases.
* Hypertrophic, restrictive or obstructive cardiomyopathy.
* Constrictive pericarditis.
* Primary pulmonary hypertension.
* Biopsy proven active myocarditis.
* Severe congenital heart diseases.
* Cardiac amyloidosis.
* Fabry disease.
* Sarcoidosis.
* Sustained ventricular tachycardia or ventricular fibrillation within 14 days of screening.
* Second or third degree heart block without a permanent cardiac pacemaker.
* Stroke within 3 months of screening, or other evidence of significantly compromised CNS perfusion.
* Hemoglobin \< 9 g/dl
* ALT \> 2 times the upper limit of normal;
* serum sodium of \< 135 mEq/dL or \> 160 mEq/dL.
* Serum potassium of \< 3.5 mEq/dL or \> 5.7 mEq/dL.
* Other acute or chronic medical conditions or laboratory abnormality which may increase the risks associated with study participation or may interfere with interpretation of the data.
* Received an investigational drug within 1 month prior to dosing.
* Patients with an allergy to iodine;
* female subject who is pregnant or breastfeeding.
* In the opinion of the investigator, is unlikely to comply with the study protocol or is unsuitable for any reasons.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 9/20/2024. Questions regarding updates should be directed to the study team contact