BACKGROUND: Valid and reliable instruments to assess family functioning, health and social support in families with heart failure constitute a cornerstone in the detection of the families' needs, in improving their functioning and in evaluating the effects of nursing interventions. AIM: To translate the three scales of the Family Functioning, Family Health and Social Support (FAFHES) questionnaire from Finnish into Danish, to test validity and reliability of the Danish version among outpatients with heart failure and to add to previous studies by reconstructing scales using confirmatory factor analysis. METHODS: A cross-sectional design was used to study a sample of 330 patients with heart failure who completed the FAFHES. The validity (dimensionality) and reliability (internal consistency and test-retest) were assessed for each of the three scales. The scales were constructed using confirmatory factor analysis. RESULTS: Patients were primarily men (76%) with a mean age of 66.5 (SD 12.5), categorised as New York Heart Association (NYHA) classification II (80%) and NYHA III (20%) for clinical severity of symptoms. In all three modified scales, construct validity was supported by the analysis. There were strong correlations within the factors, with Cronbach's alpha ranging from 0.73 to 0.95 across the three scales, and significant, though weak, correlations between most of the factors. None of the revised scales showed good model fit according to the goodness-of-fit indices used. The test-retest showed interclass correlation coefficients ranging between 0.69 and 0.86, indicating acceptable test-retest reliability. CONCLUSION: The Danish version of the FAFHES is an instrument that can be used to measure family functioning, family health and social support from the perspective of the patient with heart failure. Further testing is recommended.