The objective of this study was to assess the long-term effects of the CorCap Cardiac Support Device (CSD; Acorn Cardiovascular, Inc, St. Paul, MN) on left ventricular (LV) structure and function in patients with heart failure. Cardiac support devices, which reduce LV wall stress, have been shown to promote reverse remodeling in three different experimental models of heart failure. However, long-term effects in patients with heart failure have not been reported. We enrolled 300 patients with heart failure in the Acorn Randomized Trial, as previously reported (Ann Thorac Surg 2007;84:1226-35). Echocardiograms were obtained every six months until the last patient was followed for one year, and then annually thereafter. Standard measurements of LV volumes, ejection fraction, and sphericity index were made by a Core laboratory at the Mayo Clinic who were blinded to treatment assignment. Patients treated with the CorCap Cardiac Support Device had significant reductions in LV end diastolic volume (average difference 18.8 mL; p = 0.005) and LV end systolic volume (average difference 15.6 mL; p = 0.013) compared with the control group. Sphericity index was significantly increased in the treatment group (average difference 0.045 units; p = 0.018). These changes were maintained over three years of follow-up. The improvements in LV size and shape were observed when the CorCap was implanted concomitantly with mitral value surgery or by itself. These results demonstrate that the CorCap Cardiac Support Device has a long-term beneficial impact on LV size and shape in patients with heart failure.