The Carillon Mitral Contour System has been studied in 3 nonrandomized trials in patients with symptomatic congestive heart failure and functional mitral regurgitation. The REDUCE FMR study is a uniquely designed, double-blind trial evaluating the impact of the Carillon device on reducing regurgitant volume, as well as assessing the safety and clinical efficacy of this device. Carillon is a coronary sinus–based indirect annuloplasty device. Eligible patients undergo an invasive venogram to assess coronary sinus vein suitability for the Carillon device. If the venous dimensions are suitable, they are randomized on a 3:1 basis to receive a device or not. Patients and assessors are blinded to the treatment assignment. The primary end point is the difference in regurgitant volume at 1 year between the implanted and nonimplanted groups. Other comparisons include clinical parameters such as heart failure hospitalizations, 6-minute walk test, Kansas City Cardiomyopathy Questionnaire (KCCQ), and other echocardiographic parameters. An exercise echo substudy will also be included.