Successful long-term left ventricular assist device (LVAD) therapy necessitates a high degree of self-care. We aimed to develop an instrument that measures self-care behaviors in adult patients living with an LVAD. We used the method to develop patient-reported outcomes recommended by the US Food and Drug Administration. Prior to developing the instrument, a literature review was conducted to generate items using the middle-range theory of self-care of chronic illness as a guiding framework. A 2-round Delphi method, involving 17 clinicians with expertise in heart failure and assist devices from the Netherlands, Israel, United States, Canada, and Japan, was used to generate and select items. In the first Delphi survey, the levels of importance, relevance, and clarity of items in the instrument were evaluated. The second Delphi survey was performed to gain consensus on the final selection of items. We also examined face validity. A preliminary 37-item version of the Self-Care Behavior Scale was produced. The first panel judged 33 items as important and relevant, taking out 4 items due to vague wording and duplication and adding in 4 items. In the final 33-item version, 19 items address self-care maintenance behaviors, 10 items address self-care monitoring behaviors, and 4 items address self-care management behaviors. Patients (N = 25) did not have any difficulties understanding items and report any missing items. The 33-item Self-Care Behavior Scale for patients with heart failure having an LVAD has been developed and is ready for further psychometric testing.