Background Higher patient-caregiver mutuality is associated with improved patient and caregiver outcomes, but no studies have tested the psychometric characteristics of the mutuality scale (MS) in heart failure (HF) patient and caregiver population. Objectives To test the validity and reliability of the MS. Methods A cross-sectional design. The MS validity and reliability were tested with confirmatory factor analysis (CFA) and hypothesis testing, and with Cronbach's alpha and model-based internal consistency index, respectively. Results CFA supported the validity of the MS in the HF patient and caregiver versions. Hypothesis testing showed significant correlations between both versions of the MS and anxiety, depression, quality of life, and self-care. Also, MS caregiver version scores correlated significantly with caregiver preparedness. Cronbach's alphas and the model-based internal consistency index ranged between 0.72 and 0.94 in both versions. Conclusions The Mutuality Scale showed supportive validity and reliability for HF patients and caregivers.