The purpose of this study is to collect long term data of the Reducer System in subjects with refractory angina pectoris.

This study is a multicenter, multi-country three-arm prospective and retrospective investigation in up to 400 subjects conducted at a maximum of 40 investigational centers. Arm 1 will include eligible prospective subjects. Arm 2 will include subjects who were previously enrolled and treated with the Reducer during the COSIRA (Coronary Sinus Reducer for Treatment of Refractory Angina) study. Arm 3 will include subjects who received a Reducer under CE Mark (unrelated to the COSIRA study).

Inclusion Criteria - ALL Arms:

• Subject has been informed about the study and provides written informed consent prior to enrollment
• Subject is willing to comply with specified follow-up evaluations

Inclusion Criteria - Arm 1:

• Symptomatic Coronary Artery Disease (CAD) with chronic refractory angina pectoris despite attempted optimal medical therapy
• Subject has limited treatment options for revascularization by Coronary Artery Bypass Grafting (CABG) or by Percutaneous Coronary Intervention (PCI)
• Evidence of reversible myocardial ischemia
• Left Ventricular ejection fraction (LVEF) greater than or equal to 30%
• Male or non-pregnant female

Inclusion Criteria - Arm 2:

• Subjects previously implanted in the Reducer (treatment) arm of the COSIRA study

Inclusion Criteria - Arm 3:

• Subjects in whom the Reducer was implanted under CE Mark (unrelated to the COSIRA study), prior to enrollment in the Reducer-I study

Exclusion Criteria - Arm 1:

• Acute coronary syndrome within three months prior to enrollment
• Recent successful revascularization by PCI or CABG within six months prior to enrollment
• Recent unsuccessful PCI (no relief from symptoms) within 30 days prior to enrollment
• Unstable angina (recent onset angina, crescendo angina, or rest angina with electrocardiogram [ECG] changes) during the 30 days prior to enrollment
• Decompensated congestive heart failure (CHF) or hospitalization due to CHF during the three months prior to enrollment
• Severe chronic obstructive pulmonary disease (COPD) as indicated by a forced expiratory volume in one second that is less than 55% of the predicted value
• Subject cannot undergo exercise tolerance test
• Subject cannot undergo 6-minute walk test
• Severe valvular heart disease
• Subject with pacemaker electrode in the coronary sinus (CS)
• Subject with recent placement of a new pacemaker or defibrillator electrode in the right atrium within 3 months prior to enrollment.
• Subject having undergone tricuspid valve replacement or repair
• Chronic renal failure (serum creatinine >2 mg/dL), including subjects on chronic hemodialysis
• Moribund subjects, or subjects with comorbidities limiting life expectancy to less than one year
• Known severe reaction to required procedural medications
• Known allergy to stainless steel or nickel
• Magnetic Resonance Imaging (MRI) planned within 8 weeks after Reducer implantation
• Currently enrolled in another device or drug trial that has not completed the primary endpoint or that clinically interferes with the current study endpoints

Angiographic Exclusion:

• Mean right atrial pressure greater than 15mmHg
• Subject with anomalous or abnormal CS anatomy (e.g., tortuosity, aberrant branch, persistent left superior vena cava [SVC])
• CS diameter at the site of planned Reducer implantation less than 9.5 mm or greater than 13 mm

Subjects with refractory angina pectoris who demonstrate objective evidence of reversible myocardial ischemia, who have limited or no options for revascularization, or subjects who have received the Reducer in the COSIRA study, or under CE Mark prior to the REDUCER-I study.