Objective: The study objective was to evaluate in a prospective, randomized, multicenter trial the safety and efficacy of mitral valve surgery with and without the CorCap cardiac support device (Acorn Cardiovascular, St Paul, Minn) in patients with New York Heart Association Class II to IV heart failure. Background: Although mitral valve surgery has been performed successfully in patients with heart failure, the safety and long-term efficacy have not been established in a multicenter prospective trial. Cardiac support devices that reduce ventricular wall stress and promote beneficial reverse remodeling have been proposed as a new treatment option as a stand-alone procedure and as an adjunct to mitral valve surgery. Methods: A subgroup of 193 patients were enrolled in the mitral valve repair or replacement stratum of the Acorn Clinical Trial; 102 patients were randomized to the mitral valve surgery alone group (control) and 91 patients were randomized to mitral valve surgery with implantation of the CorCap cardiac support device. Patients were followed for a median duration of 22.9 months. Results: For the entire mitral valve surgery group, the 30-day operative mortality rate was only 1.6% at 30 days. Mitral surgery was associated with progressive reductions in left ventricle end-diastolic volume, left ventricle end-systolic volume, and left ventricular mass, and increases in left ventricle ejection fraction and sphericity index, all consistent with reverse remodeling. Recurrence of clinically significant mitral regurgitation was uncommon. Quality of life, exercise performance, and New York Heart Association functional class were all improved. Finally, the addition of the CorCap cardiac support device led to greater decreases in left ventricular end-diastolic volume and left ventricular end-systolic volume, a more elliptical shape, and a trend for a reduction in major cardiac procedures and improvement in quality of life compared with mitral surgery alone. Conclusions: These findings suggest that there is clear benefit to the surgical elimination of mitral regurgitation and that there is additional benefit with the CorCap cardiac support device. Given the improvement in left ventricle structure and function, along with a low mortality rate, physicians should strongly consider offering mitral valve surgery in combination with the CorCap cardiac support device to patients with heart failure who are on an optimal medical regimen. © 2006 The American Association for Thoracic Surgery.