COSIMA: COronary SInus Reducer for the Treatment of Refractory Microvascular Angina

Inclusion Criteria: * Age ≥ 18 and ≤85 years * Chronic coronary syndrome (including patients with anginal equivalents) refractory angina CCS class III-IV despite guideline-directed medical therapy * Evidence of reversible ischemia on non-invasive testing * Evidence of microvascular disease as diagnosed invasively by at least one of the following: 1. index of microvascular resistances (IMR) \>25 and/or 2. coronary flow reserve (CFR) \<2.0) with fractional flow reserve (FFR)\>0.8. * Willingness to participate and ability to understand, read and sign the informed consent document before enrollment in the trial. Exclusion Criteria: Subjects presenting at least one of the following criteria will not be enrolled in the trial * Recent (within 3 months) acute coronary syndrome * Recent (within 6 months) revascularization by percutaneous coronary intervention (PCI, stent) or coronary artery by-pass surgery (CABG) * Recent (within 30 days) unsuccessful PCI * Decompensated congestive heart failure (CHF) or hospitalization due to CHF during the last 3 months * Left ventricular ejection fraction of \<30% * Mean right atrial pressure \>15mmHg * Anomalous or abnormal CS anatomy (e.g., tortuosity, aberrant branch, persistent left superior vena cava \[SVC\]) as demonstrated by angiogram * CS diameter at the site of planned Reducer implantation greater than 13mm or less than 9.5mm 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 * Severe valvular heart disease * A pacemaker electrode in the coronary sinus * Tricuspid valve replacement or repair * 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 medications * Known allergy to stainless steel or nickel * Need for Magnetic Resonance Imaging (MRI) within 8 weeks after reducer implantation * Contraindication to dual antiplatelet therapy * Female of childbearing potential (last menstruation within the last 12 months or who did not undergo tubal ligation, ovariectomy or hysterectomy)