Heart failure (HF) self-care is key to managing symptoms, but current HF knowledge instruments are at risk for social desirability bias (ie, tendency to respond in a way that is viewed favorably). Vignettes may be a useful method to mitigate this bias by measuring knowledge via scenarios in which individuals with HF are invited to respond to fictional characters' self-management problems rather than disclosing their own practices. The aims of the study were to develop and test the content validity of vignettes measuring individuals' knowledge of HF symptom self-management. The study had 3 phases. In phase 1, two vignettes were developed. One focused on psychological symptom self-management (ie, anxiety, depression), and the other focused on physical symptom self-management (ie, edema, fatigue). In phase 2, the research team and lay experts made improvements to the vignettes' readability. In phase 3, five HF self-care nurse experts evaluated the vignettes' clarity and importance with a 3-point Likert-type scale using Delphi methods. We calculated the vignettes' content validity using the scale-level content validity index. The final content validation encompassed 2 Delphi rounds (phase 3), yielding a scale-level content validity index of 0.92 and 0.94 for the psychological and physical symptom vignettes, respectively. These results indicate excellent initial content validity. The content of vignettes measuring individuals' knowledge of HF symptom self-management is valid based on the opinions of nurse experts. The vignettes offer a promising method to assess knowledge about HF self-care management without the pressure of disclosing individual patient practices.