Heart Failure Optimization Study

Inclusion Criteria: Phase 1 (Registry phase) * Patients (≥18 years old) who were prescribed the WCD ≤ 10 days post-discharge after hospitalization for a primary reason of new onset HF (≤30 days since first HF hospitalization), with ischemic or nonischemic cardiomyopathy, and have used the WCD for no more than 30 days. * Patients who had an EF ≤ 35% during index hospitalization (must be last measurement if performed multiple times). Phase 2 (Study phase) * Patients who completed Phase 1 and used a WCD for 90 ± 14 days. Exclusion Criteria (both phases): * Patients under 18 years old. * Patients who have an active unipolar pacemaker. * Patients with a physical or mental condition that could impair their ability to properly interact with the device. * Patients currently participating in another clinical study. * Patients with any skin condition that would prevent wearing the device. * Patients with an advanced directive prohibiting resuscitation. Exclusion criteria (Phase 2) * Patients who have a QRS duration of ≥135 ms and are planned for cardiac resynchronization therapy. * Patients with recent myocardial infarction or coronary revascularization (since start of WCD wear; i.e. 0-90 days of WCD wear).