PREVENT is a prospective, multi-center, non-randomized study that is designed (1) to assess the incidence of HM II pump thrombosis in the current era when recommended practices for clinical management are adopted, and (2) to identify the risk factors associated with pump thrombosis events. The recommended practices are focused on implantation technique, anticoagulation regimen, pump speed and blood pressure management. All consecutive patients receiving a HM II implant will be considered for this study.