The aim was to describe the psychological functioning of parents of school-age children with heart disease (HD) in a large-scale, transnational evaluation of parent dyads across the spectrum of cardiac diagnoses and a range of psychosocial domains. Parents of children with HD attending routine out-patient cardiology follow-up visits completed questionnaires assessing their mental health, coping, and family functioning. Parents (1197 mothers and 1053 fathers) of 1214 children (mean age: 12.6 years; S.D. 3.0 years; median time since last surgery: 8.9 years) with congenital or acquired HD from three centers each in the UK and the USA participated (80% response rate). Parents of children with milder HD demonstrated few differences from healthy norms and had significantly lower scores on measures of illness-related stress and post-traumatic stress than parents of children with single ventricle conditions or cardiomyopathy. Parents in these latter two diagnostic sub-groups had significantly higher levels of anxiety and depression than healthy norms but did not differ on other measures of family functioning and coping skills. There were few differences between parents from the UK and the USA. Agreement between mothers and fathers within a dyad was highest for the measure of frequency of illness-related stressors (ICC = 0.67) and lowest for anxiety (ICC = 0.12). CONCLUSION: Our results suggest two different pathways for the long-term psychological well-being of parents of children with HD: on the one hand, more complex HD is associated with poorer long-term psychosocial outcomes; in contrast, there are also grounds for optimism, particularly for parents of children with less complex conditions, with better psychological outcomes noted for some groups of parents compared to previously reported early psychosocial outcomes. Future work needs to identify factors other than disease severity which might explain poorer (or better) functioning in some parents of children with more complex HD. What is Known: * Parents of children with congenital heart disease report elevated levels of anxiety, depression, and stress after cardiac surgery in infancy. * Maternal mental health problems can have an adverse impact on the psychological adjustment of the child with congenital heart disease. What is New: * Parents of children with milder forms of heart disease do not differ from healthy norms in the longer term and psychological outcomes are better than might be expected from early findings. * More complex diagnoses, particularly functional single ventricle conditions and cardiomyopathy, are associated with poorer long-term psychosocial outcomes for parents.