 Subjects participating in the study can expect to be actively involved in the study for two years after implantation and followed for life thereafter. The screening procedures take up to two days, depending on the specific evaluations necessary to determine candidacy. Pre-surgical exercise is conducted for at least two weeks. The implantation surgery itself lasts one day, with three to seven days of post-surgical hospitalization. Following an eight-week exercise program and a twelve-week training program, subjects are discharged from the active rehabilitation phase. They are followed quarterly for one year, and then annually thereafter. 