Coronary Sinus Reducer for Treatment of Refractory Angina - COSIRA

Inclusion Criteria: 1. Patient is older than 18 years of age 2. Symptomatic CAD with chronic refractory angina pectoris classified as Canadian Cardiovascular Society grade III or IV despite attempted optimal medical therapy for thirty days prior to screening 3. Patient has limited treatment options for revascularization by coronary artery bypass grafting or by percutaneous coronary intervention 4. Evidence of reversible ischemia that is attributable to the left coronary arterial system by Dobutamine Echo 5. Left ventricular ejection fraction greater than 25% 6. Male or non-pregnant female (NB: Females of child bearing potential must have a negative pregnancy test) 7. Patient understands the nature of the procedure and provides written informed consent prior to enrollment 8. Patient is willing to comply with specified follow-up evaluation and can be contacted by telephone Exclusion Criteria: 1. Recent (within three months) acute coronary syndrome 2. Recent (within six months) successful PCI or CABG 3. Unstable angina (recent onset angina, crescendo angina, or rest angina with ECG changes) during the thirty days prior to screening 4. De-compensated congestive heart failure (CHF) or hospitalization due to CHF during the three months prior to screening 5. Life threatening rhythm disorders or any rhythm disorders that would require placement of an internal defibrillator and or pacemaker 6. 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 7. Patient cannot undergo exercise tolerance test (bicycle) for reasons other than refractory angina 8. Severe valvular heart disease 9. Patient with pacemaker or defibrillator electrode in the right atrium, right ventricle, or coronary sinus 10. Patient having undergone tricuspid valve replacement or repair 11. Chronic renal failure (serum creatinine \>2 mg/dL), including patients on chronic hemodialysis 12. Moribund patients, or patients with comorbidities limiting life expectancy to less than one year 13. Contraindication to required study medications that cannot be adequately controlled with pre-medication 14. Known allergy to stainless steel or nickel 15. Contraindication to having an MRI performed (NB: Cardiac MRI subset patients only) 16. Currently enrolled in another investigational device or drug trial that has not completed the primary endpoint or that clinically interferes with the current study endpoints 17. Mean right atrial pressure higher than or equal to 15 mmHg 18. Patient with anomalous or abnormal CS as demonstrated by angiogram. Abnormality defined as: Abnormal CS anatomy (e.g., tortuosity, aberrant branch, persistent left SVC) and/or; CS diameter at the site of planned reducer implantation less than 9.5 mm or greater than 13 mm