Inclusion Criteria:

• Age ≥ 18 years of age.
• Able to provide written informed consent and willing to participate in all required study follow-up assessments.
• Symptomatic CAD with refractory angina defined as CCS class II to IV, despite optimal tolerated medical therapy for more than 3 months.
• Abnormal coronary microvascular function indices: CFR ≤ 2.5 and/or HMR ≥ 2.5 & or coronary blood flow (CBF) response to acetylcholine ≤ 50%.  

Exclusion Criteria:

• Recent (within 3 months) acute coronary syndrome.
• Patients with prior coronary artery bypass surgery.
• Unstable angina (recent onset angina, crescendo angina, or rest angina with ECG changes) during the last 30 days.
• Subjects in cardiogenic shock (systolic pressure < 80mm/Hg, on vasopressors or intraaortic counter pulsation) at the time of consenting. Subjects who recover from cardiogenic shock by the time of consenting are eligible.
• Obstructive CAD on coronary angiography (> 70% stenosis or 50-70% stenosis with iFR < 0.89 or FFR < 0.8 in epicardial artery).
• Inability to perform invasive coronary flow evaluation and/or measure CFR and HMR in the LAD.
• Severe valvular heart disease.
• Left Ventricular Ejection Fraction (LVEF) < 30%.
• Decompensated congestive heart failure (CHF) or hospitalization due to CHF during the last 3 months.
• Patient with a pacemaker electrode in the CS.
• Mean right atrial pressure > 15 mmHg.
• Anomalous or abnormal CS anatomy (e.g., tortuosity, aberrant branch, persistent left superior vena cava (SVC) 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.
• Severe chronic obstructive pulmonary disease (COPD) indicated by a forced expiratory volume in one second that is less than 55 percent of the predicted value.
• Tricuspid valve replacement or repair (tissue or mechanical).
• Chronic renal failure (serum creatinine > 2mg/dL), and or on chronic hemodialysis.
• Moribund, or with comorbidities limiting life expectancy to less than one year.
• Known severe reaction to required procedural medication.
• Known allergy to stainless steel or nickel.
• Magnetic Resonance Imaging (MRI) within 8 weeks of Reducer implantation.
• Participation in another ongoing investigational trial.
• Additional factors deemed unsuitable for trial enrollment per discretion of principal investigator.
• Inmates.

Eligibility last updated 4/22/22. Questions regarding updates should be directed to the study team contact.