U.S. patients prescribed a commercially available WCD (ZOLL LifeVest) will be approached by a letter from the sponsor which summarized the study purpose and procedure. Once a patient signs a consent form to participate the study, he or she will receive three questionnaire from University of Rochester, the coordination and data center for the WEARIT registry, at the time enrollment, at 3 month and 12 month follow-up, respectively. At 3 and 12-month follow-up, the physician of the patient will be contacted to provide information on arrhythmias, and interim events (ICD, CRT or LVAD implantation, heart failure episode, death), and to send us related hospital reports and echocardiogram reports to assess the improvement in left ventricular function.