The purpose of this study is to evaluate the efficacy of CS Reducer implantation in patients with HFpEF and CMD on left ventricular filling pressures, specifically invasive measurement of PAWP during standardized exercise.

Inclusion Criteria

• Age ≥ 18
• Able to provide written informed consent and willing to participate in all required study follow-up assessments
• Clinical indicated coronary angiography with invasive CRT testing within 9 months prior to enrollment. Abnormal CFR of ≤ 2.5
• Symptomatic HFpEF defined by (PAWP>15mmHg at rest and /or PAWP>25 mmHg on exertion) during clinically performed Right heat catheterization with exercise performed within 6 months of enrollment or during screening visit (if not performed clinically in the last 6 months).
• Non-Obstructive CAD (≤ 50% stenosis in epicardial vessels and/or iFR>0.89 or FFR>0.8 in vessels with 50 to 70% stenosis)

Exclusion Criteria

• History of left ventricular (LV) ejection fraction <50%
• Significant epicardial CAD (angiographic stenosis ≥70% or positive FFR or iFR in any major epicardial coronary artery
• Significant valvular heart disease (more than moderate regurgitation and or stenosis)
• Primary cardiomyopathies (hypertrophic, infiltrative or restrictive)
• Constrictive pericarditis
• Severe myocardial bridging
• Stiff left atrial syndrome
• Pregnancy
• Recent (with 3 months) acute coronary syndrome
• Subjects in Cardiogenic shock (systolic pressure<80mm/Hg)
• NYHA Class III or IV heart failure decompensated HF
• Mean right atrial pressure at rest >15 mmHg
• Anomalous or abnormal CS anatomy (e.g. tortuosity aberrant branch persistent left superior vena cava as demonstrated on angiogram
• CS diameter at the site of planned implantation greater than 13mm or less than 9.5 mm as measured by angiogram.
• Known severe reaction to required procedural medications
• Known allergy to stainless steel or nickel
• Magnetic Resonance Imaging (MRI) within 8 weeks after Reducer implantation
• Chronic renal failure (serum creatinine>2mg/dL)
• Severe chronic obstructive pulmonary disease (COPD) as indicated by forced expiratory volume in one second that is less than 55% of the predicted value or need for home daytime oxygen
• Pacemaker electrode/lead in the coronary sinus
• Moribund or with comorbidities limiting life expectancy to less than one year
• Current or past participation within a specified timeframe in another clinical trial, as warranted by the administration of this intervention.
• Inability or unwillingness of individual to give written informed consent.
• Additional factors deemed unsuitable for trial enrollment per discretion of the Principal Investigator
• Inmates